Seneca Grey tank draining issues

[Dchafe]

Hi all, we have been on a 2 month road trip and besides a couple of small issues, the trip has been problem free. Throughout the trip, I’ve noticed slow drain issues in the grey tank. I’ve cleaned out the hair, but the issue persists. We noticed the shower pan fills after about 3-5 minutes. When that happens I can hear a “gulping” noise near the bathroom sink, but no other sinks fill. I replaced the air gap cap under the kitchen sink. I’m not aware of any other air gap. We have a 2020 Seneca 37HJ. As soon as I open the grey tank it drains. Anything else I’m not think of ?

[Plumberman]

There is another "air admittance valve" (air cap) under my bathroom sink and I would suspect under yours as well. The shower is the lowest drain on the system so the water will not back up into the the other sinks. My shower has a "waterless trap" (no U bend) that has a rubber duck bill type of check valve in it. If the rubber is torn or misshapen it will not allow the air to pass through it as the water is draining. But I would suspect the air admittance valve first.

[Dchafe]

I can’t find one under the bathroom sink. I suspect it may be on the roof? There’s no other place I can think of it could be. When we get back I’ll have to check further.

[Plumberman]

The one on the roof should just be an open pipe under the wind cover. No air admittance valve there. Keep me posted, this is interesting.