I'm a full time RVer. My kitchen(only) gray water tank is constantly open and draining. But recently I began to notice that the tank is registering 3/4 full. At first I thought bad guage but then while doing some dishes the water began to not drain from my kitchen sink. I tried to fill the tank(remaining 1/4) with hot water, let it drain, repeat, fill/drain but it's not draining any lower than 3/4 full.Surely gray my tank isn't 3/4 full of residue? And now that I think about it, it was registering empty just a couple of weeks ago so I'm pretty sure it couldn't fill up that fast. I use screens on my sinks to prevent anything large from going down them.Any ideas?

Fill a sink and have someone drain it while you watch. My guess is your sensor is dirty and isn't working.

I don't think you read my post thru. First, the water is backing up out of my sink drain. Second, I can see the end of the drain hose and nothings coming out and I did clear the hose so that's not it. If I remove the cap at the RV gray tank opening... nothing but a trickle and the gauge reads 3/4 full.

Have you tried just closing and opening the grey valve to see if something has started clogging up at that point?

Might try this. Let tank drain for a while. Get an old hose and take off the male end. Open valve and put a big bucket under outlet. Turn the hose on and force hose up into Grey tank, and see what happens. If there is a blockage in the tank drain that may help to remove it. If you have hot water available you might use it. If that helps, the next time you are towing, but some hot water with detergent in tank to let help to flush out tank.

Sounds like the tank cutout lodged in the pipe.I had a trailer a few years ago that had the same problem, turned out to be a piece of floor lino that had dropped into the tank.

Gray tank won't drain | Good Sam Community

30 Replies

jplante4
Explorer II
Oct 01, 2015
Read the OP's post. His grey tank is kitchen sink only so the shower won't be backing up. Check this

1. Verify that the tank vent (pipe to the roof) is free of debris.
2. Check that there's no blockage in the tank drain (the aforementioned tank cutout).
3. If you suspect that the tank is actually filling with crud, see this.
Bobbo
Explorer III
Oct 01, 2015
Galley gray tank, not main gray tank. The shower won't be involved.

OP, I am afraid you will have to push a plumber's snake up the drain. That will be messy.

I, also, had a plug from a cut-out. Mine was in the black tank where they cut the circle on the top of the tank for the toilet drain. I didn't know what the problem was until I had owned the RV for about 3 years. I was at home draining the tanks with my Flojet Macerator and using a clear section so I could watch for clear water flow. I saw the circular piece of plastic fall into the clear section. No problems since that came out.
Big_Katuna
Explorer II
Sep 30, 2015
Is the shower backed up? It will back up before the sink.
BFL13
Explorer II
Sep 30, 2015
AFAIK leaving the tank open to drain is a bad idea, at least with black tanks, so I suppose it is the same with the galley grey tank.

IIRC you are supposed to let it build up some, so when you do open the valve there is enough there to do a real dump and clear it all out.

Our kitchen grey readings are usually higher than it really is with gunk on the sensors, but with yours being actually plugged up, you need either a physical poke at it, or some kind of Draino.

The ice cube trick only works if you can get ice cubes down the drain (by-passing the sink connection underneath?) and you can drive around so the ice cubes can do their work.
Lynnmor
Explorer II
Sep 30, 2015
Are you by chance using a garden hose to drain? Did you remove the 3" cap when you checked?
mogman
Explorer
Sep 30, 2015
Sounds like the tank cutout lodged in the pipe.

I had a trailer a few years ago that had the same problem, turned out to be a piece of floor lino that had dropped into the tank.
Dr_Quick
Explorer II
Sep 30, 2015
Might try this. Let tank drain for a while. Get an old hose and take off the male end. Open valve and put a big bucket under outlet. Turn the hose on and force hose up into Grey tank, and see what happens. If there is a blockage in the tank drain that may help to remove it. If you have hot water available you might use it. If that helps, the next time you are towing, but some hot water with detergent in tank to let help to flush out tank.
Beaker
Explorer
Sep 30, 2015
Have you tried just closing and opening the grey valve to see if something has started clogging up at that point?
cephoto
Explorer
Sep 30, 2015
I don't think you read my post thru. First, the water is backing up out of my sink drain. Second, I can see the end of the drain hose and nothings coming out and I did clear the hose so that's not it. If I remove the cap at the RV gray tank opening... nothing but a trickle and the gauge reads 3/4 full.
Big_Katuna
Explorer II
Sep 30, 2015
Fill a sink and have someone drain it while you watch.

My guess is your sensor is dirty and isn't working.

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Gray tank won't drain

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