Unforgivable: losing the cap on the water tank

[killerme]

I had to take out the fresh water tank and it's housing and the back seat to do some welding but I seem to have lost the cap underneath the tank.  Does anyone have any idea how I could replace it?  Its not difficult to replace the other cap (for removing the used water) but I can't find either the tank or the cap anywhere.

[TONYT25T25]

What diameter is it, you maybe able to get away with using a blanking screw plug they use on garden hose attachments, or even a bottle cap.

[killerme]

I'm currently going through every bottle in the house! lol
 

[R0B]

Maybe try an ad in the wanted section.

[killerme]

Aha! The top from a large bottle of Gaviscon works! Cheers everyone.

[TONYT25T25]

Peppermint or Aniseed flavour    

[Dobble]

I needed one of these when I fitted my water tank, I found that a Plasson water fitting has the same thread so used one of those with a Plasson bung and a dowty washer.