TITLE A STOP TAP FIELD OF THE INVENTION [0001] The present invention relates to a stop tap. In particular, although not exclusively, the invention relates to a stop tap for receiving and restricting water flow from a mains water supply to an appliance, such as a washing machine. BACKGROUND TO THE INVENTION [0002] In many cases, a tradesperson, or home handyman, will use a sealing element such as Teflon tape to seal a female threaded inlet to a male thread. However, this type of seal is prone to many disadvantages. For example, using too much of a sealing element can result in the female thread splitting. Not using enough tape to create a seal can result in leaks when the connection has water pumped through it. [0003] Certified Australian innovation patent AU2011101764 attempted to improve on features of a basic stop tap, or stop cock valve designed to overcome the problems described above. [0004] However, the above described design suffers from numerous drawbacks. In particular, this structure is prone to forming an ineffective seal with the valve seat and can cause leaking. A further drawback resides in the long term wear on the valve closure member which also results in a poor seal with the valve seat. 1 [0005] Another particular drawback lies in that the inlet connection nipple is typically glued and screwed into place. As a result, if the glue has not been applied correctly or sufficiently, the stop tap will leak as the glued thread provides the seal between the inlet nipple and the body of the valve. [0006] A further issue resides in the installation of the valve. Typically, when the valve is installed, a plumber will adjust the angle and/or position of the outlet without undoing the swivel nut which causes the glue to crack and thus cause the valve to leak. [0007] Furthermore, the inlet is always subject to pressure such that any issues with the glue will cause the valve to leak whether the valve is in a closed or open position. [0008] Accordingly, based on the above, there is a clear need for an improved stop tap and an improved method of installing a stop tap. OBJECT OF THE INVENTION [0009] It is an object of the present invention to overcome and/or alleviate one or more of the disadvantages of prior art systems or provide the consumer with a useful or commercial choice. SUMMARY OF THE INVENTION [0010] In one aspect, although not necessarily the only aspect or the broadest aspect, the invention resides in a stop tap to be installed between a mains water supply and a water receiving appliance, the stop tap comprising: 2 a body having an inlet, an outlet, and a water flow passage through the body connecting the inlet to the outlet; a valve closure member received in the body, the valve closure member movable between a closed position to close the flow passage and an open position to open the flow passage, an outside surface of the valve closure member in sealing contact with an inside surface of the body; and operating means connected to the valve closure member for selectively moving the valve closure member between its closed and open positions; the inlet of the body including a female internally threaded swivel nut for engagement with an externally screw threaded supply nipple to install the stop tap; and a sealing insert provided in the swivel nut of the inlet to form a seal between the externally male screw threaded supply nipple of the mains water supply and the inlet; wherein the valve closure member includes a ceramic disc cartridge. [0011] Preferably, the stop tap further includes an inlet nipple received in the inlet; the inlet nipple having an external screw thread which engages an internal screw thread of the body; and wherein the inlet nipple is fitted with an O-ring which forms a seal between the inlet and the inlet nipple. [0012] Preferably, the sealing insert comprises a sealing grommet. 3 [0013] Preferably, the sealing insert is composed of a rubber material. [0014] In another form, although not necessarily the only or broadest form, the invention resides in a method of installing and using a stop tap, the method comprising: installing the stop tap by threading the inlet onto a water mains supply nipple; connecting the water receiving appliance to the outlet of the stop tap; and selectively operating the operating means of the valve to allow water to flow to the water receiving appliance or to restrict water from flowing to the water receiving appliance. [0015] Further features of the invention will become apparent from the detailed description below. BRIEF DESCRIPTION OF THE DRAWINGS To assist in understanding the invention and to enable a person skilled in the art to put the invention into practical effect, preferred embodiments of the invention will be described by way of example only with reference to the accompanying drawings, in which: FIG. 1 a cross-sectional side view of an embodiment of a stop tap, according to an embodiment of the present invention; and FIG. 2 is an exploded view of the stop tap shown in FIG. 1. 4 DETAILED DESCRIPTION OF THE DRAWINGS [0016] The present invention relates to a stop tap to be installed between a mains water supply and a water receiving appliance comprising a male externally screw threaded nipple and a downstream appliance or fitting so as to enable isolation of the mains water supply and disconnection of the downstream appliance or fitting. [0017] Elements of the invention are illustrated in concise outline form in the drawings, showing only those specific details that are necessary to understanding the embodiments of the present invention, but so as not to clutter the disclosure with excessive detail that will be obvious to those of ordinary skill in the art in light of the present description. [0018] In this specification, adjectives such a first and second, top and bottom and the like may be used solely to distinguish one element or action from another element or action without necessarily requiring or implying any actual such relationship or order. Words such as "comprises" or "includes" are intended to define a non-exclusive inclusion, such that, a method or apparatus that comprises a list of elements does not include only those element but may include other elements not expressly listed, including elements that are inherent to such a method or device. [0019] The embodiment shown in FIG. 1 illustrates a stop tap 100. The stop tap 100 includes a valve body 105 which has an inlet nipple 110 which receives water from a mains water supply and an outlet 115 out of which water is supplied to an appliance or fitting. The valve body 105 also defines a flow passageway 120 connecting the inlet nipple 110 to the outlet 115. The 5 flow passageway 120 provides a path for water to flow through to enter the inlet 110 and exit to the appliance via the outlet 115. [0020] The valve body 105 further includes a swivel nut 125 with an internally threaded portion for mounting the stop tap 100 to the supply pipe nipple (not shown). Advantageously, only the swivel nut 125 needs to be rotated to mount the stop tap 100 to the supply rather than the entire body of the stop taps of the prior art. [0021] The inlet nipple 110 further comprises an externally threaded portion 130 for threaded engagement for securely engaging with the valve body 105. Before installation within the valve body 105, the inlet nipple 110 is fitted with an O-ring 135 which provides a seal between the body 105 and the inlet nipple 110. Advantageously, the O-ring 135 eliminates the cracked glue of some prior art stop taps. Further advantageously, if a plumber were to adjust the angle and/or position of the outlet 115 without undoing the swivel nut 125 causing the glue to crack, the O-ring 135 provides an extra seal to prevent any leaks. [0022] Housed within the swivel nut 125 is a sealing insert defined as a sealing grommet 140. The sealing grommet 140 faces outwardly from the inlet 110 to engage with and seal to the water supply to prevent leaking once the stop tap 100 has been installed and is in use. The sealing grommet 140 is typically conical in shape and composed of a rubber material. However, it will be appreciated by a person skilled in the art that the sealing grommet 140 may comprise any suitable shape and be composed of any suitable material. [0023] The inlet nipple 110 further defines a valve seat 145. The embodiment shown includes a valve closure member which is defined as a 6 ceramic disc cartridge 150 in this embodiment. Once assembled, the ceramic disc cartridge 150 is sealingly engaged with the valve seat 145. Advantageously, the sealing engagement created between the valve sear 145 and the ceramic disc cartridge 150 cannot be broken without completely removing the ceramic disc cartridge 150 from the valve body 105. [0024] The ceramic disc cartridge 150 is operable by an operating means shown to be a rotatable tap handle 155 secured to the ceramic disc cartridge 150 by a pin 160. The rotatable tap handle 155 moves the ceramic disc cartridge 150 from a closed position to an open position (or an open position to a closed position) to allow or restrict water flow through the flow passageway 120. Advantageously, as the inlet nipple 110 forms the valve seat 145 for the ceramic disc cartridge 150, the thread of the inlet nipple and O-ring 135 are not subject to pressure while the ceramic disc cartridge 150 is in the closed position. [0025] As shown, the stop tap 100 is of a "T" shape design such that an axis 165 of the outlet 115 is perpendicular to an axis 170 of the inlet nipple 110. However, a person skilled in the art will appreciate that the shape of the stop tap 100 and the relationship of the axes 155, 160 can vary to suit varying requirements. [0026] FIG. 2 shows an exploded view of the stop tap 100 described in FIG. 1. In assembly, the valve body 105 receives the ceramic disc cartridge 150 into the flow passageway 120 and the ceramic disc cartridge 150 is then fitted with the rotatable tap handle 155 which is secured with a securing pin 160. The swivel nut 125 threadingly engages with the inlet nipple 110 which is fitted with the O-ring 135 and the sealing grommet 140 to provide a seal and 7 prevent leaking once the stop tap 100 is installed. The swivel nut and inlet nipple apparatus 125, 110 is then threadedly engaged with the body 105 to form the completed stop tap 100. [0027] Once the stop tap 100 is assembled, the swivel nut 125 of the inlet 110 can be fitted to a mains water supply nipple (not shown) and an appliance or fitting (not shown) can be connected to the outlet 115. The rotatable tap handle 155 can then be selectively rotated to operate the ceramic disc cartridge 150 to allow or restrict water to flow from the inlet 110 through the passageway 120 to outlet 115 to supply water to an appliance. [0028] The above description of various embodiments of the present invention is provided for purposes of description to one of ordinary skill in the related art. It is not intended to be exhaustive or to limit the invention to a single disclosed embodiment. As mentioned above, numerous alternatives and variations to the present invention will be apparent to those skilled in the art of the above teaching. Accordingly, while some alternative embodiments have been discussed specifically, other embodiments will be apparent or relatively easily developed by those of ordinary skill in the art. The invention is intended to embrace all alternatives, modifications, and variations of the present invention that have been discussed herein, and other embodiments that fall within the spirit and scope of the above described invention. 8