Internal vent for holding tank. Madness or not?

[CarlF]

Reef earlier. You'll sail faster and keep the vent out of the water.

Seriously, as long as you don't use a filter that can't get wet a little seawater down the vent hose isn't going to hurt anything. It's not any different than the seawater put in there by the toilet. Do get a vent that faces aft so water isn't pushed in.

And it's almost always possible to take the vent tube high enough on its route to to the vent fitting to form a loop. Go from the tank up to the underside of the deck or a high spot like the cockpit coaming. Then go sideways to the hull. Even 12" inboard from the rail the deck is considerably higher than the water surface when heeled.

[mikecambrai]

To increase the efficacy of the anaerobic process, it is common practice to fit a small solar powered pump which bubbles air to the bottom of the tank via a fitting at the top of the tank. This should be in the form of a pipe laying across the bottom with many holes to spread the air around the mix, or several pipes fed into the top and reaching the bottom of the mix.
Oxygen is used in land applications, but air will certainly help vastly in our marine environment.

[bsurvey]

its methane gas and flammable


you boat will smell like an industrial porta potty


not a good idea. remove a stanchion, drill a hole in the base and vent it out through the stanchion so it can't be seen

[Mike Banks]

Firstly, it is madness to allow gasses from the holding tank to enter the hull. H2S has about the same toxicity as the gas used to kill oprisioners at San Quentin--so it is thye last thing one needs in ones boat. Then there is methane--highly explosive if it ever builds up in sufficient quantity.

BUT--you do not have to exir the hull at the bow. They have PIPES which can run alom=ng the deck shelf to a suitable exit point--although mine was always directly above the tank after passing through a carbon filter--which needs to be replaced every year or so--but the carbon itself can be boiled then hot-dried--and thereby re-sued indefinitely. MOst folks simply replace a cartridge the moment one notices any smell from tghe deck outlet. My outlet was behind a stanchion, close to the pump-out portal with its screw-in lid. It was out of toe-range and rope range there.

So--definitely madness.

[SailFastTri]

Originally Posted by bsurvey

its methane gas and flammable


you boat will smell like an industrial porta potty


not a good idea. remove a stanchion, drill a hole in the base and vent it out through the stanchion so it can't be seen

Not a great idea to vent through stanchion, IMHO.
1) Holding tank vents need to be big (at least 1" ID) to allow good airflow.
2) What if you overfill the tank?
3) If a vent gets clogged by insects or poo, you need to be able to clean it out easily.
4) It could weaken the stanchion.