Black tank plumbing question
I know I have a black water vent on the top of the roof of the MH . Why do I also have an AAV (air admittance valve) under the bathroom sink? Aren't. they used for the same function? I'm confused.
Forum Discussion
Almost right. The AAV under the sink, on either the black tank or the gray tank, vents the sink's drain pipe after the P trap. If it wasn't there, as the water drained out of the drain pipe into the waste tank, it would pull a vacuum that would suck the water out of the P trap, allowing the tank fumes to come up through the sink drain.
