Previous owners of my boat have tried allsorts to get the weedtrap to seal properly so air isn't sucked in preventing water from circulating inside properly.
Vaseline has been used around the outer seal but last year even that was not working and the seal itself is still to this day in perfect condition. Probably due to the fact its been caked in vaseline for years!!

Anyway I traced the problem not to the outer seal, but to the bolt and wingnut. After the lid is put in place I fitted a rubber grommet on the bolt and put the wingnut over the top of the grommet.  Absolutely no problems ever since.
Some of you may have already tried this, but just in case anyone is having problems getting a good seal, give it a go.  

--Last edited by flashheart on 2008-07-02 12:17:43 --

Quote :

Flashheart wrote : to get the weedtrap to seal properly

If you go to http://www.nimue.co.uk/ and click on 'Notices', you'll see a diagram of our weedtrap.  

Ours was leaking (hiss hiss) until we made sure that the central washer was both (a) fitted and (b) nice and squishy.

although as brianlj has purchased a new weed trap with a tight fitting screw in top we have done away with the wingnut etc - and its see through so we can stand and watch the water gurgling through it and through our new see through non collapsing pipes - could be more fun than cruising!