venting a holding tank

[Walt G]

Hi. Wintertime projects, again. I'm looking for info on adding a second vent hose to the poly holding tank in my 37c. The tank does not have an access hole, and I'd rather not add one unless I have to. So, a few questions: does anyone know of some type of self-tapping and self-sealing fittings that could be used to add a vent line? You know, just sort of drill a big hole and tap the fitting in? Next question: if the only sensible way to add a fitting is through an access hole so it can be fastened from both sides, has anyone had any luck adding an access hole in a poly tank that (absolutely, positively) does not leak? Lastly, has anyone ganged holding tanks together for reasons of space (or because, like me, you hate to remove a slightly undersized tank that still works pretty well and doesn't smell too badly. Thanks, in advance, for your replies. Capt Walt S/V Moonshine.

 

[Ralph Johnstone]

In all likelyhood it can be done

........... if you take a look at how your level sensor is attached to the top of thetank. If you don't have a sensor, it is installed with a pipe flange arrangement. I think you could fabricate the same thing from 3/4" thick poly which is cut into the shape of a 1" diameter flange with six bolt holes. The 1" centre hole is then threaded with a 1" NPT die. I would suggest using #8 SS screws to attach the flangeI have used Permatex 2 in the past as a gasket sealant and found it to be one of the only things that permanently sticks to poly. Although this should never leak, I would probably want to locate this only on the TOP of the tank to try to avoid having any hydrostatic pressure on it.Best of Luck,s/v Island Hunter

 

[Peggie Hall/Head Mistress]

SeaLand offers a fitting...

It's a type of compression fitting that doesn't require access to the inside of the tank. Give 'em a call at 800-321-9886