FORUM RULES UPDATED - The forum rules have been updated to continue to provide a friendly and safe environment for our member community. Please take a moment to review the updated rules and our terms of use and privacy policy. Click here for Forum Rules which has links to the 'terms of use' and 'privacy policy'.
If it's the same unit I'm picturing in my head, then get a standard thread 1/2" PVC cap.<br />If not, take the cap off, and go to a boatyard, and see if they have one.<br />Another atempt would be the hardware stores.
im in Scotland we get a thing here in a tube the plumbers use fir sealing toilets its like a claer rubber soultion in a tube try your local iron mongers its clear silicon put that on the threads and pray
The plastic seal washer behind the cap is probably missing. Sometimes you can get them to seal good enough by simply wrapping the cap with plumber's tape before you screw it in.