[Richard]

Vince,

Look under the kitchen sink. Follow the black drain pipe. It will exit the sink, flow through a P trap, and then you will see a round cylinder about 2 inches in diameter. Mine had two vertical slots in it. I taped the slots closed.

If you go to Home Depot or Lowes, look for air admittance valves in the plumbing section. It will show you exactly what you are looking for. I found them on the three sinks. I did not look on the washing machine connection, nor the shower. When you see them in Lowes, it is easy to see how they are supposed to work. They contain a flimsy rubber diaphragm that is supposed to seal when pressure is applied to the underside, but open when vacuum is applied. It is pretty easy to see how that would fail to work over a period of years.

The tape made a big difference.

[Ozarkguy]

Has anyone ever tried to replace the P-Trap and valve with one of these??
http://www.hepvo.com

[Richard]

Interesting concept. I can see how it would serve the purpose of both the p trap and the air admittance valve. I am not sure if it would be a restriction to catch things.

[Ozarkguy]

Cheap enough to try tho....and would gain a bunch of cabinet space..

[HoosierDaddy]

Good observation Richard, One of the things mentioned on their web-site is that it will NOT catch that ring or ear rings like a P trap would.

It seems to me that soap and hair will eventually cling enough to it that it could let some sewer gas escape.

[Richard]

Even after sealing the air admittance valves, we still would get a smell if someone flushed a potty while I was driving. When looked at the Microflush manual, it states in fine print that they recommend a small ventilation fan for sealed tanks. When I look at the way the hopper empties, you may have an open path while flushing. Anyway, I replaced the normal roof vent caps with the windvane type that spins to orient with the wind.

I did that in September, and six weeks and 3000 miles later I am happy to report that it cured the smell issue.

They were cheap, about thirty bucks each. It took more time to get out the ladder than it did to install them.

Here is the type I used. Cyclone vent