[font size="3"]A simple trick I picked up from some CG.
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At CGs with full hookups it's convenient to leave the gray water dump valve open so you don't have to empty the tank with heavy use. However, with small pressure variations due to sewer use by other campers and fan use in our CL we occasionally get some sewer gas back into the camper. The AAVs in the CL operate on very small differential pressures and they're sometimes not perfect. A small dip in the sewer hose solves this problem by creating an external gas trap. The picture is one example, but anything that provides a 3" rise will work. A 4x4 block, a drop before the accordion style hose elevators, etc.
If you're unfortunate enough the CG will do it for you by elevating the sewer connection. >:(
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Thanks Charlie. Good tip.
For those mere mortals, an AAV is an air admittance valve that is installed after the P-trap under the sink. It is a one way valve that lets air in to vent the trap. In houses we usually have vents through the roof to accomplish this. The AAV can stick open a little and let sewer gasses back in. The little dip in the sewer hose forms another p-trap which blocks the sewer gas.
David
Meh. I try to make sure I have some grey water to flush after a black tank dump, just for the sake of the hose. The only time I would leave they grey open is if someone were actively using the shower.
Also, it would be too easy to forget, and leave the grey open when dumping black, which the backflow up into they grey tank would be not desireable.