OK so I am at the end of my ideas. On our recent trip to Florida I had a problem with the galley sink not draining. At first I thought it was clogged below the sink. I didn't have a small plunger so I ended up pulling the trap. Low and behold it was clean as a whistle but I did notice that there was some back pressure when I took it off. So it seemed it was a vent problem. I don't think the gray tank was completely full. I put everything back together and the sink now drained OK. DW then took a shower and the sink started gurgling and burping and the trailer started to fill with tank smell. I went out and drained the gray water tank and all was well again. This was only after 1 day of water usage. Seems outside the norm to have used 20 gallons of water in one day since we were not doing to much in the way of dishes and such. Still thinking it was a vent problem I pulled the cover off the vent and checked for blockage, nothing to see except a clear tube to water reflecting in the tank.
So.. the vent is clear, everything seems to work until the tank is about 2/3 full and then it all starts again. I am at a loss as to what to check now. Is it possible for the vent pipe itself to slip down into the tank thus creating my scenario? If so how would I even verify this has happened.
Any advice would be GREATLY appreciated.
It definitely sounds like a venting issue. My guess is there's a vent clogged somewhere, but exactly where might be tricky to track down. It could also be that the drain line to the grey tank runs uphill at some point (i.e., snapped-off support strap).
Your sink could have its own vent if it's far enough away from the holding tank. It is usually upstream from the sink drain. Also, your sink could use an air admittance valve ( http://www.diyadvice.com/diy/p.....ance-valve ) that's malfunctioning.
Additionally, I've heard it's not entirely uncommon for the shower to drain into the black tank instead of the grey tank. However, it sounds from your description like you've already determined that's not the case here. The only reason I mention that is because you may be looking down into the wrong vent/tank.
This show segment contains the install of a black+grey plumbing system in a small TT undergoing a total refit:
Mark's RV Garage Episode #9 Internet TV Series by RV Education 101
It might provide some other ideas of where the venting problem is.
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