Reginald P. Smithers III wrote:
Chuck Gould wrote:
Another useful concept to bear in mind when disposing of human waste is
that two types of bacteria eat this stuff in the holding tank.

Aerobic bacteria needs oxygen to survive. Aerobic bacteria generally
don't stink.
Anerobic bacteria emerge wihen there is no oxygen available in the
holding tank, and they tend to stink pretty badly.

Assuring the presence of some oxygen in the holding tank will help
control smells.

I have a vent for my holding tank, but I know that is not enough oxygen,
because it does stink. What system allows enough oxygen to promote
aerobic bacteria?

SeaLand makes, (I believe still) a sort of "bubbler" that can be
inserted into the holding tank.
The device pumps in air, much like an aquarium stone. Coupled with a
vent of adequate size and design, pumping a bit of air into the tank
and through the effluent will diminish the smell.

There are Aerobic bacteria additives sold for septic tanks and a marine
version developed by Peggie Hall (then sold to Raritan) that can be
added to a holding tank to reduce odors, but it would seem reasonable
that once aerobic bacteria are introduced their effectiveness would be
enhanced with adequate oxygen.