clogged holding tank vent line

[Rhendry]

One of the holding tanks on our boat is operating weirdly. When you pump dwon the toilet (electric) the water partly refills the bowl (raw water not holding tank water) and then bubbles of air start to pour through the bowl. The odor is like what I think a holding tank air would smell like. Is it possible that we have a clogged holding tank vent line? If we do, how do I fix that problem.

Your replies are appreciated.

Ralph Hendry
c/v Simplicity
2003 48' St Francis Catamaran
currently sailing Ft. Piece, FL.

[perchance]

If the vent line is plugged it would most likely cause the holding tank to collapse when you pump it out.

[sww914]

Yes, you have a clogged vent line. To fix it you have to find it, take it apart, and un-clog it.

[Nicholson58]

It may be easy. Many people use the tiny fuel tank vents with the fine screen flame arrestor. These blind over with corrosion, salt or spiders. This is the typical bad-boy. Its not intended for a holding tank but is OK-sort-of if its open. My research said 1/2" vent line with no restrictions when we did the work.

[Dave852]

I believe your holding tanks are in your keels? Attached to the stainless plate on top of the tank you will find a small hose that runs up inside your cabinet to a vent just above or below the rub rail. There you will either find a clogged filter or a trap that should not be there filled with liquid.

[sailvayu]

Am I wrong or wouldn't a clogged vent cause the sewage water water to back up? Not the raw water. I am thinking this is not a vent issue at all. What kind of electric head is this, knowing that would help. Also if you flush the head with someone outside the boat near the vent they should hear some air moving and smell the sewage some. If you do not get that then I may wrong and it could be the vent.