Holding tank bloat

The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.

Gordon B

Veteran Member
Jan 10, 2015
Vessel Name
Vessel Make
41' Defever
Hi to all,
I replaced the holding tank in our 87 Defever 41. The old one cracked I believe because of a clogged vent line. The vent line was repaired and all was fine. I could hear the vent when we pumped out. I noticed the vent line dripping, so I went below to check the tank. I discovered it was bloated; it also is tilted downward(toward the inlets) a little.
Is the bloating caused by pressure and if the tank is tilted will that screw things up. Any remedies? We live aboard and this has become critical.

Are you sure it's not full and has partially plugged the vent. I would carefully remove the deck fill and see if that relieves any pressure. Let us know what happens when you do this.
I am starting to believe that as the tank was filling up that it may have tilted toward the vent and plugged it. I did open the deck fill and got no release of gasses.
A couple of points on your holding tank and vent lines to consider,

Two kinds of bacteria inhabit holding tanks: aerobic and anaerobic. The former require oxygen to exist and reproduce; without it, they’re goners. Aerobic bacteria break down organic matter, creating as a byproduct carbon dioxide, which is odorless. Conversely, anaerobic bacteria thrive in a low- or no-oxygen environment. The by product they create is a variety of gases, including sulfur monoxide and sulfur dioxide. which impart the pungent odor (and methane and carbon dioxide, which are odorless).

1) In order to provide adequate airflow, vents should be larger than the typical 5/8-inch hose. Ideally, the inside diameter should be a full inch;
2) Vents should also be plumbed to opposite sides of the vessel, enabling cross flow, in a direct line with as few bends and dips as possible.
3) Remember, the aerobic bacteria, which digest waste and don’t produce odor in the process, require oxygen. So providing it is often the most effective and simplest approach.
4) If passive cross ventilation can’t be achieved, a holding tank aeration system is a viable alternative. (Like the Sani Tank System)
5)The larger the exterior vent can be, the better.

Cheers Steve
Top Bottom