Grey Tank Drain

[Lostdog]

OK, folks....when we are parked for any length of time I leave the gray tank valve open and the black tank valve closed until it needs to be dumped, just like a lot of people do. Close the gray to fill when it's getting close to time to dump black so as to have a flush for the hose.

Since about last February every so often the gray tank will fill even though the valve is wide open. It let's us know when the shower starts filling! Yuck! (can't rely on sensors) I was thinking the tank may have some sort of construction debris in it that causes a blockage but also have noticed a "burp" just before it begins to drain. When the gray has stopped up I usually need to dump the black, then refill the black with fresh water, close the exterior valve I installed on the sewer outlet, open the gray valve then open the black valve to "backflush" the gray and then the gray will break loose and drain. But before I open the exterior valve I hear that "burp". It also seems to happen when we have used the washer/dryer for a couple of loads. But not always.

Could it be that the gray tank in not vented properly? Or a vacuum breaker isn't working. How the heck to you test that???

[RudysWorld]

I never leave gray tank open so can't deal with that part of the question.
I did find the piece of tank that was cut out for the drain connection in the drain tube early on, so you might want to check for that. I am fairly new to Rving and like the idea of the pressure of a full gray tank to flush everything out.

[Iggy]

I have heard others having a piece of the tank hole that fell into it blocking to exit of water.

If you do have a washer/dryer setup look at the washer drain pipe and I believe that is the vent to the roof for the grey water tank. Your may be different.