AU2020203711A1 - Holding tank for liquid containment - Google Patents

Abstract

: A tank for hazardous liquids including a tank or container body defining a tank outlet is disclosed. The tank body comprises an inner side wall and inner base, 5 and an outer side wall and an outer base surrounding the inner side wall and inner base. The inner and outer side walls and base provide a dual containment structure that persists liquid from leaking out of the containment structure. The inner base slopes towards the tank outlet at an angle which is sufficient to cause liquid to drain completely from the inner base of the container body. 10 Figure 7 for publication V0 INCLINED IBC STAND 60 FOR FULL DRAINAGE SLOPED FOR FOR FULL DRAINAGE i _14740/A WIDTH4 SIDE VIEW Figure 7 20 IBC LIFT Figure 8

Description

V0

INCLINED IBC STAND FOR FULL DRAINAGE 60

SLOPED FOR FOR FULL DRAINAGE i

_14740/A WIDTH4 SIDE VIEW

Figure 7

20

IBC LIFT

Figure 8

HOLDING TANK FOR LIQUID CONTAINMENT FIELD

This disclosure relates to a holding tank for liquid containment. The disclosure extends to a plant including a holding tank for liquid containment.

This invention relates particularly to a holding tank for containment of hazardous liquids to avoid uncontrolled spillage of hazardous chemicals for safety and environmental reasons. It will be convenient to describe the invention with reference to example application, but it is to be clearly understood that the invention is capable of broader application.

DEFINITION

In the present description and claims, the term "comprising" shall be understood to have a broad meaning similar to the term "including" and will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. This definition also applies to variations on the term "comprising" such as "comprise" and "comprises".

BACKGROUND

Holding tanks for holding or carrying hazardous liquids such as acid or alkali, poisonous liquids, and environmentally compromising liquids such as lubricant, or hydraulic oils are known in the art. Some examples of holding tanks used for this purpose are decanters and others are mother daughter tanks.

Typically, the holding tank might comprise a tank body for receiving a liquid and a valve towards an operatively lower region of the tank for enabling liquid within the tank to be selectively dispensed into another vessel or pipeline. The liquid can then be transported in the other vessel or pipeline for its intended use and application.

Some shortcomings or limitations of prior art holding tanks include the following:

• They have a single wall structure and do not form a safe barrier or containment for resisting leakage of liquid from the tank if the wall is breached or fails in any way. • They generally have a horizontal floor and, as a result, when liquid is drained from the tank, a residual amount of liquid remains on the floor of the tank that is not easy to remove. • They often have a sight glass filled with liquid from the tank to determine the level of liquid in the tank, and this side glass is thus positioned outside of the tank. This poses a weakness as the liquid in the sight glass is effectively held outside the containment provided by the tank and this creates additional opportunities for liquid to leak from the sight glass onto the surrounding floor.

The risks identified above with prior art holding tanks pose a safety risk could lead to serious injury or death. Further, any leaks could also lead to environmental damage.

Workplace health and safety issues are becoming ever more important in Western countries and accordingly, there is a constant need to improve safety in industrial workplaces. This is particularly the case in plants where dangerous and hazardous materials are being handled. There is also a demand from plant owners to provide more effective safety solutions in plants to reduce the risk of industrial accidents and the legal consequences arising from these accidents including prosecution and legal liability.

The reference to prior art in the background above is not and should not be taken as an acknowledgment or any form of suggestion that the referenced prior art forms part of the common general knowledge in Australia or in any other country.

SUMMARY OF DISCLOSURE

Applicant has recognised that it would be beneficial if a holding tank for hazardous liquids could be devised that reduced a risk of hazardous liquids spilling out of the tank onto the surrounding floor and posing a safety risk and/or environmental risk.

According to one aspect of this disclosure, there is provided a tank for liquid containment, the tank including: a container body defining a tank outlet comprising: an inner side wall and inner base, and an outer side wall and an outer base surrounding the inner side wall andinnerbase; wherein the inner base slopes towards the tank outlet for directing liquid on the inner base towards the tank outlet.

The inner base may slope down towards the outlet at an angle that is large enough to cause liquid to drain from the inner base of the container body.

While the inner base slopes down towards the outlet for directing liquid towards the outlet, the outer base does not slope down and is substantially horizontally extending. That is the outer containment provided by the outer wall and outer base provides retention only in the event of breach and is not required to direct liquid towards an outlet.

Optionally, the inner base may slope at an angle of 1.5 degrees to 10 degrees, e.g. at a slope of 1.5 to 5 degrees towards the outlet. In one example form the inner base slopes at an angle of about 2.5 degrees.

In contrast to the inner and outer bases, the inner and outer side walls may extend substantially parallel to each other and be spaced a distance apart from each other.

The tank outlet may be formed in the inner and outer side walls towards the inner base of the tank body.

The tank may further include an outlet valve at the tank outlet mounted on the inner side wall towards the inner base. The outlet valve may also be mounted on the outer side wall towards the outer base. The outlet valve enables liquid to be selectively discharged from the tank outlet, e.g. into another container or pipeline for use or transport.

Conveniently, the outlet valve may be a ball valve interchangeable between an open and closed position although it will be appreciated that other types of valves capable of releasing liquid from the tank on demand may also be used.

Instead the tank may further include a flange for operative connection to another flange on the outlet for forming a flanged connection for enabling liquid to be dispensed from the tank.

Further instead, the tank may include a pipe fitting for connecting the tank to another pipeline, pump or tank. In particular, the pipe fitting may be a union having at least one screw threaded connection for coupling to an adjacent pipe or fitting, e.g. a fitting for a pipeline, tank or pump.

Optionally, the tank may further include at least one liquid level indicator for indicating the level of liquid within the tank to a user.

The liquid level indicator may include a sensor for sensing the level of liquid in the tank and then a visual indicator for indicating the level of liquid based on the level of liquid sensed by the sensor.

The liquid level indicator may comprise an ultrasonic level sensor and a visual display for displaying the level sensed by the ultrasonic level sensor to an operator.

The liquid level indicator may also include a mechanical level indicator, either in addition to the ultrasonic sensor or in place of the ultrasonic sensor, that senses the level of the surface of the liquid by means of a mechanical element and visually presents the liquid level to an operator outside of the tank.

The mechanical level indicator may comprise a float element on the liquid that is in operative connection with an element that extends over the inner and outer side wall and down the outer side wall on the outside of the tank to a level marker.

This way the position of the level marker on the outside of the tank, when calibrated, indicates the level of liquid within the tank.

The tank may further include a tank support including a support base on which the outer base is mounted.

The tank support may comprise formations for engaging a lifting device for generally handling and transporting the tank.

In one form, the formations may be in the form of forklift engaging formations for receiving forks from a forklift for moving and lifting the tank.

The forklift engaging formations may comprise a plurality of linear members that are laterally spaced apart from each other. The plurality of spaced members may extend parallel to each other and be mounted on an underside of the outer base of the tank body.

The tank may include a forklift guard for protecting the tank body and outlet against damage from the forklifts being used to lift and manoeuvre the tank.

To form the forklift guard, the forklift engaging formations may project radially out beyond the extent of the outer base in the direction of length of the forklift formations. This holds the forklift formation spaced away from the perimeter of the outer wall so that the forklift formations cannot damage the tank and its various components and features described above.

The tank may further include lifting lug points fixed to the outer side wall, e.g. of the tank body or dual containment cylinder, for operative connection to a crane for handling and moving the tank.

The tank body may have a top wall mounted on an upper end of the inner side wall. The top wall may comprise a single member, i.e. different from the side wall which is of dual layer construction, because dual containment is not required on the top of the tank.

The tank may further include a supply tank support, e.g. a supply tank platform, positioned above the tank body for supporting a supply tank in a position above the tank body for transferring liquid into the tank body.

The supply tank support may be sloped so that a liquid within a supply tank that is mounted on the supply tank support drains towards an outlet of the supply tank when it is emptied.

The supply tank support may be mounted on the top wall of the tank body. Preferably, the supply tank support is supported directly and solely on the top wall of the tank body, and thus the weight of a supply tank mounted on the supply tank support is carried by the inner side wall, this weight being transmitted through the supply tank support and top wall.

Optionally, the supply tank support may comprise a rectangular frame of four members.

The supply tank support may further include locating formations for locating and holding a supply tank in position thereon. Each locating formation may comprise a corner piece, e.g. on the rectangular frame, having a raised edge for providing lateral retention.

The tank may further include a coupling arrangement for operatively coupling an outlet on a supply tank to an interior space defined by the inner side wall whereby to enable liquid to be transferred from a supply tank to the interior space of the tank body. In one form, the coupling arrangement may comprise a camlock connection providing a secure coupling from the supply tank to the holding tank.

The inner and outer side walls and bases of the tank body may be formed of a polymeric material. The material will be selected and engineered to retain the range of liquids intended to be received within the tank body.

The inner and outer walls and inner and outer bases may be configured to meet the spillage angle, retainment capability construction material and compound drainage requirements of AS3780.

The tank support may be fabricated from fibre reinforced plastic or steel, e.g. mild steel. Similarly, the supply tank support may be fabricated from the aforementionedmaterials.

The tank may include an overflow for enabling liquid to be discharged from the tank volume inside the inner side wall and inner base when the tank volume within the inner side wall is filled with liquid. The overflow directs overflow liquid into the space between the inner and outer side walls.

The overflow may comprise a spout positioned towards an upper end of the tank body that extends from an overflow inlet through or over the inner wall of the tank body to an outlet positioned between the inner and outer side walls. This way overflow liquid is retained by the outer side wall and does not spill onto the floor around the holding tank.

The tank may include at least one inspection hatch on the tank body for enabling inspection of the interior of the tank.

The tank may include at least one pressure relief valve mounted on the tank body for venting gas within the tank body when the internal pressure rises above a threshold level.

Optionally, the pressure relief valve may be mounted on the hatch.

The tank may include a drip tray with a transparent hose for safe decanting of liquid from the container body. The drip tray also includes a drain plug for draining any retained liquid from the drip tray.

The tank may include a leak detection port for enabling an operator to detect a leak of liquid through the inner side wall and base.

The tank outlet may be configured such that a valve can be interchanged with a flange and a threaded connection whereby to enable the tank to be adapted for different applications.

Optionally, the tank may be used as a decanter for decanting off liquid to be used into other containers or tanks as and when required.

Instead, the tank may also be used as a mother and daughter tank where liquid is supplied from a larger mother tank to a plurality of smaller daughter tanks for distribution or use.

The invention extends to a plant including a holding tank as defined in the preceding aspect of the invention.

The holding tank may include any one or more of the features of the holding tank defined in the preceding aspect of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

A holding tank, in accordance with the invention, may manifest itself in a variety of forms. It will be convenient to hereinafter describe in detail a preferred embodiment of the invention with reference to accompanying drawings. The purpose of providing this detailed description is to instruct persons having an interest in the subject matter of the invention how to carry the invention into practical effect. However, it is to be clearly understood that the specific nature of this detailed description does not supersede the generality of the preceding broad description. In the accompanying diagrammatic drawings:

Figure 1 is a perspective view of one embodiment of a tank in accordance with the disclosure;

Figure 2 is a front view of the tank in Figure 1;

Figure 3 is a schematic side view of a similar tank to that in Figure 1;

Figure 4 is a cross sectional view of the tank in Figure 3;

Figure 5 is a front view of the tank in Figure 1 being handled by a forklift truck;

Figure 6 is a perspective view of the tank of Figure 1 having a storage tank mounted thereon;

Figure 7 is a front view of the tank of Figure 1 and storage tank shown in Figure 6;

Figure 8 is a schematic front view of the storage tank mounted on the tank in Figure 1, showing the storage tank being handled by a forklift truck;

Figure 9 is a schematic perspective view of a mechanical liquid level indicator that is used on the tank of Figure 1; and

Figure 10 is a perspective view of a tank in accordance with a second embodiment of the invention.

DETAILED DESCRIPTION

Figures 1 to 4 illustrate a tank in accordance with one embodiment of the disclosure. In these drawings, reference numeral 10 refers generally to the tank.

Broadly the tank 10 comprises a container body 12 defining an internal liquid space 14. The container body 12, in turn, comprises an inner side wall 20 and base 22 and, also includes an outer side wall 26 and base 28. The inner and outer side walls 20 and 26 are spaced a distance apart from each other which in the illustrated embodiment is about 41mm but this measurement may be different for different tanks and different applications. The outer side wall 26 and outer base 28 circumferentially surround and enclose the inner side wall 20 and base 22 providing a dual container structure which has two separate and independent layers. Both layers need to be breached for liquid contained within the internal liquid space 14, e.g. hazardous liquids, to leak laterally or downwardly out of the container body 12.

Further, the inner base 26 slopes down from one side of the container body 12 to another at a slope angle that is sufficient to cause liquid to flow downwardly to drain from the container body 12. Optionally, the inner base 26 may slope down at an angle of 1.5 to 5 degrees, e.g. about 2.5 degrees. As illustrated in the drawings, the inner and outer side walls 20 and 22 extend parallel to each spaced a short distance apart from each other. The inner and outer bases 26 and 28 are spaced apart from each other but the outer base is substantially horizontally extending which is different to the sloped inner base 26.

The feature of inner and outer side walls 20 and 22 that provides the dual container structure for the tank body is manufactured in accordance with Australian standard AS3780. This standard sets out criteria for the spillage angle, retainment capability construction material and compound drainage requirements.

Conveniently, the tank body 12 may be in the form of a cylindrical configuration with a circular outer base 28, and cylindrical inner and outer side wall 22 and 26, extending vertically up from the outer base 28.

The choice of material for the inner and outer walls of the tank body would typically be based on the nature of material to be contained within the tank and its physical properties. For several applications, the tank body may conveniently be formed of a polymeric material that is resistant to corrosion by the liquids that are to be stored in the tank.

The tank 10 further includes a tank outlet towards the bases 24 and 28 of the body 12 and an outlet valve 30 mounted on the inner and outer container walls 22 and 26 at the tank outlet. The outlet and valve 30 are positioned and arranged adjacent to a lowest point of the sloping base 24 for draining residual liquid from the tank efficiently. The outlet valve 30 enables liquid to be selectively discharged in a controlled fashion to the outside of the tank body 12 from the internal liquid space 14 within the tank body 12. Conveniently, the valve 30 is a ball valve, e.g. an ASAHI TYPE 21 ball valve although other types of valves and connectors may also be used.

The tank outlet may be configured such that a valve can be interchanged with a flange or a threaded pipe fitting such as a union at the outlet to adapt to different applications and different customer needs and requirements.

Further, the tank body 12 has a top wall 36 for enclosing off a top of the internal liquid space 14 towards an upper end of the side walls 20 and 26.

The tank 10 also includes a liquid level indicator including a sensor for sensing the level of liquid in the tank 10 and then a visual indicator for indicating the level of liquid based on the level of liquid sensed by the sensor. The level indicator in this disclosure is designed and configured so that the liquid is always retained within the dual containment structure and does not provide a weakness through liquid can breach the dual wall construction. This is a noteworthy safety feature because it ensures retention of hazardous liquid within the containment provided by the tank.

In the illustrated embodiment, one liquid level indicator comprises an ultrasonic level sensor and a visual display indicated generally by numeral 42 for displaying the sensed level to an operator. Ultrasonic sensors are available commercially and the structure and function of these sensors would be known to persons skilled in the art. Accordingly, the sensors will not be described in greater detail in this detailed description.

Optionally, the tank 10 also includes a mechanical level indicator 44, which is shown in some detail in Figure 9, and comprises a float element on the liquid that is in operative connection with a flexible element that extends over the wall of the tank body 12 and down the outside of the tank body 12 to a level marker on the flexible element. The position of the level marker on the outside of the tank body 12 when calibrated thus indicates the level of liquid within the interior liquid space 14 of the tank body 12. As mechanical indicators are known, their structure and function would be known by skilled persons and will not be described in further detail in this specification.

The tank 10 further includes a support structure in the form of a tank support indicated generally by 50 associated with the tank body 12. The tank support 50 is the structure on which the tank body 12 and, in particular, the outer base 28 thereof, is directly mounted.

In the drawings, the tank support 50 includes lifting formations 54 in the form of forklift base for engaging a lifting device for generally handling and transporting the tank 10. In one form, the lifting formations 54 are in the form of forklift engaging formations for receiving forks from a forklift for moving and lifting the tank 10. The forklift engaging formations 54 comprise a plurality of linear members that are laterally spaced apart from each other and positioned beneath the outer base 28 and operatively mounted thereto by fastening elements as illustrated in the drawings.

The tank includes a forklift guard for protecting the tank body and outlet against damage from the forklifts being used to lift and manoeuvre the tank. To form the forklift guard, the forklift engaging formations project radially out beyond the extent of the outer base in the direction of length of the forklift formations. This holds the forklift formation spaced away from the perimeter of the outer wall so that the forklift formations cannot damage the tank and its various components and features described above.

The tank may also include crane lugs for engaging a lifting device for generally handling and transporting the tank 10.

The tank 10 further includes a supply tank platform 60 positioned above the tank body 12 for supporting a supply tank in a position above the tank body 12 for transferring liquid from the supply tank into the tank body 12. In the illustrated embodiment, the supply tank platform 60 is sloped (in a similar manner to the inner base 28 of the container body 12) so that liquid within a supply tank mounted on the supply tank platform 60 drains towards an outlet of the supply tank and drains the tank fully when emptied leaving no residual liquid.

In the illustrated embodiment, the supply tank platform 60 comprises a substantially rectangular frame that is sized and configured to locate and support a supply tank of a certain standard size. In the illustrated embodiment, the frame is open and has storage container locating and retaining formations 62 in each corner thereof. The configuration of the locating formations includes upright edges that provide for lateral retention and are shown in Figure 1 of the drawings. Further, two of the frame members, e.g. on opposed sides, are inclined to provide the slope for draining residual liquid from the storage tank as discussed above.

The tank 10 further includes a coupling arrangement 70 for operatively coupling an outlet on a supply tank to the interior space 14 of the tank body 14 whereby to enable liquid to be transferred from the supply tank to the interior space 14 of the tank body 12. In the illustrated embodiment, the coupling arrangement 70 is in the form of a camlock connection. As this type of connection is used in the industry, its structure and function would be known by skilled persons and will not be described in further detail in this specification.

The tank 10 further includes a liquid overflow 74 for enabling liquid to be discharged from the tank when the tank body 12 fills up with liquid and overflows. The overflow comprises a spout positioned towards an upper end of the tank body 12, that extends through both the inner and outer walls 22 and 26 of the tank body 12, to discharge liquid from the internal liquid space 14 to the outside of the tank body 12. The tank 10 further includes a spill tray, e.g. with a drain nut, (not shown) positioned beneath the liquid overflow 74 to catch and retain any liquid overflow from the tank 10.

The tank 10 further includes at least one pressure relief device 78 mounted on the tank body 12 for venting gas within the space 14 of the tank body 12 when the internal pressure rises above a threshold level. As the structure and function of pressure relief valves on sealed tanks would be well known in the art, they will not be described in further detail in this detailed description.

Figure 10 illustrates a tank in accordance with a second embodiment of the invention. The tank is very similar to the tank illustrated in the earlier drawings and accordingly the same reference numerals will be used to refer to the same components. The following description will focus on features that are not shown in the earlier embodiment.

In Figure 10, the tank 10 further includes an inspection hatch 90 on the top wall 36 for enabling an operator to inspect the interior space 14 of the tank 10. The pressure relief valve 78 may conveniently be mounted on the hatch 90.

Further, the tank 10 includes a drip tray 92 with transparent hose 94 for safe decanting of liquid from the body 12. The drip tray 92 conveniently includes a drain plug 96 for enabling retained liquid in the drip tray 92 to be safely drained therefrom. Further, the tank 10 includes a leak detection port for enabling an operator to detect any leakage of liquid through the inner side wall 20 and base 26 into the containment provided by the outer side wall 22.

Further, the tank 10 also includes lifting lugs 98 for enabling a crane to lift the tank 10 and move it around to facilitate handling by a crane in addition to handling by a forklift truck.

In use, the holding tank 10 in any one of Figures 1 to 10 can be handled by a forklift and moved into position on a factory floor. The forklift formations 54 on the tank support 50 enable the forklift to securely lift and manoeuvre the holding tank 10 in the manner shown in Figure 5.

The holding tank 10 can then be used to receive liquid from a supply tank and be used to dispense the liquid into other tanks, e.g. daughter tanks for application and use. A storage tank 80 is delivered on site and is then used by the forklift truck to place it on the supply tank support platform 60 in the manner shown in Figures 6 to 8. The tank 80 is held in position by the locating formations 62 which ensure the supply tank 80 is correctly positioned on the platform 60, and also laterally retained in position.

The supply tank 80 has an outlet 82 for discharging liquid therefrom and this is coupled to the coupling arrangement on the holding tank 10. The liquid from the supply tank 80 can then be gravity fed into the holding tank 10. The sloping orientation of the platform 60 ensures that the supply tank 80 is fully emptied and there is minimal residual liquid left in the supply tank 80 when it is allowed to flow out. Thereafter, the supply tank 80 can be uncoupled from the holding tank 10 and lifted off the platform 50 and removed using the forklift in the manner shown in Figure 8.

The holding tank 10 can then be used to dispense liquid therefrom through the discharge or outlet valve 30 on the tank outlet. The level indicators 42 and 44 indicates the level of liquid within the tank to an operator.

When the holding tank 10 is required to be used for holding a different liquid, that discharge valve 30 is opened and the existing liquid within the liquid space 14 is allowed to drain fully. The sloping inner and outer bases 24 and 28 ensure that the liquid drains fully and there is little or no residual liquid remaining on the inner base 24 of the holding tank 10.

An advantage of the holding tank described above with reference to the drawings is that containment of hazardous liquids within the boundary of the tank is assured by the double or dual containment tank body structure. These breaches of the tank body could be caused by either failure of the walls or a nozzle leak at the tank outlet. Any liquid breaching the inner side wall is retained within the outer side wall and this resists spillage onto the surrounding area. The sloping inner and outer base on the tank body ensures complete drainage of the holding tank when it is emptied. There are no residual chemicals left on the bottom of the tank.

The complete drainage of the holding tank 10 confers the following working advantages.

Different chemicals can be stored consecutively in the holding tank without the risk of any residual amount of the first chemical being mixed with the incoming second chemical.

Further, the residual chemical is removed from the tank and is not wasted.

The tank can be handled safely once it has been emptied with confidence that all residual hazardous chemical has been removed.

Yet further, the embodiments illustrated above provide a convenient supply tank platform that is positioned above the tank body. The platform has locating formations that are configured to locate a supply tank being mounted thereon for transferring liquid therefrom to the holding tank. Yet further, the sloping supply tank platform enables liquid to be fully drained from the supply tank when it is emptied so that no residual liquid is left in the supply tank. Once again, this reduces waste and avoids the situation where a supply is being handled and moved which contains some residual liquid therein.

Another advantage of the embodiments illustrated above is that the holding tank can be easily handled and moved around by a forklift truck. The tank has forklift engaging formations in the tank support that facilitate this handling of the tank using a forklift.

Yet another advantage is that the tank has a level indicator that enables an operator to reliably know the level of liquid in the holding tank without having to physically open the tank and look inside it. This is very important for a tank that is designed for holding hazardous liquids. Further, the level indicator functions without breaching the liquid containment of the tank body such as occurs with a side glass holding liquid from the tank. It has two systems that sense or measure the level of liquid in the tank and then present this information to an operator on the outside of the tank.

Yet further, the supply tank support, e.g. platform, is configured so that it is convenient for a supply tank to be mounted on the supply tank support using a forklift truck.

It will of course be realised that the above has been given only by way of illustrative example of the invention and that all such modifications and variations thereto, as would be apparent to persons skilled in the art, are deemed to fall within the broad scope and ambit of the invention as is herein set forth.

It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not limiting. Changes in detail or structure may be made without departing from the basic elements of the invention as defined in the following claims.

Claims (8)

CLAIMS:

1. A holding tank for liquid containment, the tank including: a tank body comprising, an inner side wall and inner base configured for liquid containment, and an outer side wall and an outer base surrounding the inner side wall and inner base that are also configures for liquid containment, the tank body forming a tank outlet, wherein the inner base slopes towards the tank outlet for directing liquid on the inner base towards the tank outlet.

2. A holding tank according to claim 1, wherein the inner base slopes down towards the outlet at an angle of 1.5 to 5 degrees.

3. A holding tank according to claim 1 or claim 2, including a valve, a pipe coupling or a flange coupling at the tank outlet for selectively releasing liquid from the tank.

4. A holding tank according to any one of claims 1 to 3, further including at least one liquid level indicator for indicating the level of liquid within the tank to a user, and wherein the liquid level indicator includes an ultrasonic level sensor or a mechanical level sensor.

5. A holding tank according to any one of claims 1 to 4, further including a supply tank support positioned above the tank body for supporting a supply tank in a position above the tank body for transferring liquid into the tank body.

6. A holding tank according to claim 5, wherein the supply tank support is sloped so that a liquid within a supply tank mounted on the supply tank support drains fully from the supply tank.

7. A holding tank according to claim 5 or claim 6, wherein the supply tank support further includes locating formations for locating and holding a supply tank in position thereon.

8. A holding tank according to any one of claims 1 to 7, wherein the tank support includes lifting formations for engaging a lifting device for handling the tank.