Originally Posted by Robin Hein
Herk, I just looked under my sink, and there doesn't appear to be anything that you have posted on your link from your last post. There is a black box under the sink that is just below the sink drain, not sure what that is. I do have 2 vents on the top of the trailer I am presuming they are for a vent of some sort as well.
A photo will help us. The two roof vents are for your holding tanks.
An Air Admittance valve looks like this. It is most likely located under the bathroom sink for the shower drain.
There could also be rubbish in the trap. Access to the trap would be from a storage compartment (perhaps behind a false wall.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
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