gray water backing up.

[LAWBC]

This thread has been very helpful and the Hepvo Waterless Valve appears to be the fix. But this brings up one more thing that is missing....go to your shower and look at the cross bars in the drain. I have tried to put a toe stopper in our A/S shower, (to soak my feet while having a shower) and it appears the center is not threaded to accept one. I have tried both 5/16th and 3/8th sizes. If anyone has success putting one in, please let us know.
LEAKPRF STOP 5/16-2 RAPFT [03-4821] : Lasco - Plumbing Parts!
However, failing that, I'm thinking something like this bad boy, Shower Drain Plug, as it will stop the air and water (reminds me of those old Thermos bottle plugs). Now I'm thinking.... "would that move the problem to the bathroom sink"?

[nickermax]

Hi
I had the same problem in my 2006 28 International. The grey tank was not vented properly and kitchen sink water would come into the shower. To correct the problem I had to run a vent hose from the grey tank to the main vent stack and the problem was solved. This is a common problem with poor tank venting in Airstream trailers.

[batman]

I used 3 of the HEPVO valves in the restoration of my 64 Safari. They work great and as stated the extra room the give you is a huge bonus in our small space. For 24.99 at VTS you can't beat it.