HeadMistress wrote:
The vent line has everything to do with creating AEROBIC conditions in the tank.... when it's short enough, straight enough, and of sufficient diameter to allow a free exchange of air with the gasses in the tank.* But the "standard" 5/8" ID vent line can't do that if it's more than about 18" long. A vertical line even that short cannot do that because the gasses in the tank are heavier than air they don't rise, fresh air doesn't fall, so the twain never meet. 5' is about the maximum length that will allow a tank to "breathe."
Aeration can indeed be an excellent solution to holding tank odor, but rarely needed in tanks smaller than about 40 gallons unless the tank location makes a short straight relatively horizontal vent line impossible.
So there must be at least one other way to prevent odors.
No, only ways to make 'em unnoticeable by filtering 'em or release 'em far enough away.* * When organic matter--ALL organic matter--breaks down ANaerobically, it always generates hydrogen sulfide and sulfur dioxide, which are not only very stinky, but also highly toxic...even lethal in high enough concentration...and also methane, which is also highly toxic AND flammable, but odorless.* But when organic matter--ALL organic matter, not just sewage--breaks down aerobically it always converts to CO2, which is both harmless and odorless.* That's just a law of physics.* But the only thing that matters is whether the way odor is dealt with on your boat makes you happy.