Claims 1. A conduit device for conducting a fluid from a fluid source to a recipient, comprising a tubular portion having an inlet end and an outlet end, an inner side of said tubular portion being intended for contact with the fluid, characterized in that means are provided for adapting the surface tension of at least the fluid. 2. A conduit device as claimed in claim 1, in which said means are provided as a surface active agent introduced into the fluid, said surface active agent being capable of reducing the surface tension of the fluid. 3. A conduit device as claimed in claim 2, in which said surface active agent is provided in the form of tablet in a dispensing unit positioned near or at the inlet end of the tubular portion. 4. A conduit device as claimed in claim 2, in which said surface active agent is incorporated in the tubular portion of the conduit device, such that the surface active agent is in contact with at least the inner side of the tubular portion. 5. A conduit device as claimed in claim 2, in which the surface active agent is an additive dissolved in the material that makes up the tubular portion,or in the form of smaller or larger separate accumulations of molecules scattered throughout said material. 6. A conduit device as claimed in claim 2, in which said surface active agent is provided by means of a gel or by injection of a liquid surface active agent. 7. A conduit device as claimed in any one of claims 2 to 6, in which said surface active agent is chosen from the group of polyphenylene oxide-polyethylene oxide copolymers, polyethylene glycol esters etc. 8. A conduit device as claimed in any of the preceding claims, in which at least one part of the tubular portion has enlarged cross-sectional dimensions in relation to the remaining parts of the tubular portion, e.g. comprising at least one corrugated portion. 9. A conduit device as claimed in claim 1, in which the cross-section of the tubular portion has at least one incision. 10. A conduit device as claimed in claim 9, in which each incision is substantially V-shaped or U-shaped and/or extends in a spiral or curve. 11. A conduit device as claimed in any of the preceding claims, in which said conduit device further includes a cord member extending substantially throughout the length of the conduit device. 12. A conduit device as claimed in any one of the preceding claims, in which the outlet end of the tubular portion has a widened cross-section in relation to the remaining parts of the tubular portion. 13. A conduit device as claimed in claim 10, in which the widened cross-section is provided by at least one obliquely extending cut at the outlet end. 14. A conduit device as claimed in any one of the preceding claims, in which, additionally, means are provided for adapting the surface tension of the inner side of at least said tubular portion. 15. A conduit device as claimed in claim 14, in which said means are provided by application of a ma terial having a surface tension that is substantially the same or larger than the surface tension of the fluid on at least the inner side of the tubular portion. 16. A conduit device as claimed in claim 15, in which said material comprises a continuous layer. 17. A conduit device as claimed in claim 15, in which said material comprises at least one longitudinally extending portion. 18. A conduit device as claimed in claim 15, in which said material comprises at least one sector of the tubular portion. 19. A conduit device as claimed in any one of claims 15 to 18, in which said material is applied by means of co-extrusion with the tubular portion. 20. A conduit device as claimed in claim 15, in which said material is provided as an additive to the material of the tubular portion, the additive being capable of migrating to at least the inner side of the tubular portion. 21. A conduit device as claimed in claim 20, in which the tubular portion includes a protective layer or coating on the outer side. 22. A conduit device as claimed in any of claims 15 to 21, in which said material comprises a hydrophilic polymer, such as polyethylene-vinyl alcohol copolymer, ethylene-vinyl acetate copolymer having a high content of vinyl acetate, polyether esters, acrylate copolymers, polyether amides, polyurethanes etc . 23. A conduit device as claimed in any of claims 15 to 22, in which said material comprises at least one polyphenylene oxide, polyethylene oxide copoly- mer, alkyl- and/or arylsulphonates, polyethylene glycol ester, fatty acid ester, fluorosurfactant and/or siliconesurfactant. 24. A conduit device as claimed in claim 23, in which said material comprises at least one of PEG 400 distearate, PEG 400 dilaurate, Standapol (trademark of Cognis, Germany) , preferably Standapol 1345 and/or Standapol 1480, Pluronic (trademark of BASF Corporation, Germany), preferably Pluronic L10, Atmer (Trademark of Uniqema, the Netherlands), preferably Atmer 100, and/or Zonyl (trademark of Dupont, USA), preferably Zonyl FSO-100 and/or Zonyl FSN-100. 25. A conduit device as claimed in any one of the preceding claims, in which said means are provided by surface treatment of the inner side of the tubular portion. 26. Use of the conduit device as claimed in any of claims 1 to 25 as a hose member in connection with a collection bag. 27. A kit comprising a conduit device as claimed in any of claims 1 to 25 and a collection bag. 28. Use of the conduit device as claimed in any of the claims 1 to 25 as a hose member connecting a urinary catheter device with a urine collection bag. 29. A urinary catheter arrangement comprising a catheter device, a conduit device as claimed in any of claims 1 to 25, and a collection bag, c h a r a -cterizedin that the catheter device is an external urinary catheter for the relief of urinary incontinence . 30. A urinary catheter arrangement comprising a catheter device, a conduit device as claimed in any of claims 1 to 25, and a collection bag, c h a r a - cterizedin that the catheter device is a urinary catheter for insertion into the bladder.