Gray tank won't drain

Quick check w/o having to go on roof.....

Look under kitchen sink on drain line After the 'P' trap for a short stub pipe with an Air Admittance Valve. They just hand screw into stub pipe.
They open when draining grey tank.....small flapper inside....to keep sink drain line from pulling vacuum when draining waste tank/keeps 'P' trap from being sucked dry allowing waste tank odors inside rv.

Unscrew/remove it.......and see if waste tank drains faster/better.
Flapper is just a small air inlet. With it removed line is fully opened (1 1/2") and would act like a vent line to tank.

IF tank still drains really slow.........drain line out of tank/tank outlet is clogged vs clogged vent.

tried all suggestions that seemed appropriate... time to poke. Anyone wanna come over and help out with that? lol

cephoto: I've yet to see any of those red/yellow/green light tank level indicators work with any degree of accuracy/reliability and I don't trust them at all. OK, I agree, they do work when the vehicle is/was new or after the tanks have been power washed. (for a while) I just flushed my black/gray water tanks today but the level indicators still read full. I KNOW they are empty.

I don't mean to be arrogant or rude, it's just after years of shop training/experience, ALWAYS CHECK THE MOST SIMPLE THINGS FIRST is etched in my DNA. I wish I had all the hours back that I've spent pulling my hair out trying to diagnose a complex problem when the answer was a simple blown fuse or a flipped circuit breaker.

Remote diagnosis is always a challenge.

Chum lee

cephoto wrote:
..I am noticing that this a.m that it's drained down to 1/4 of the tank overnight....

My black tank does that. After I dump it often shows 2/3 full. Next morning (valve closed since dumping) it will show 1/3. Seems like the sensors need to dry off. About twice a year I put the wand down the toilet and give it a cleaning. Seems to be the only time I see 0 (empty). Sometimes the grey tank will show 1/3 after dumping and the next morning, with the valve still closed, it will show 0.

Try actually filling the grey tank with the gate closed and then, when full, open the gate and dump. Some Dawn dish soap and Calgon water softner does a good job of cleaning grey and black tanks.

When is the big 'poke' going to happen ?

If you do the "big poke", be at a dump station, use a long hose, hold the end of the slinky above the level of the tank, that way you can avoid the on-rush of smelly water when you clear the blockage, then after you've pushed the hose up into the grey tank, pull the hose, lower the slinky, rather quickly into the drain. Well, that would be my recommendation anyway.

ok, for those of you that seem to think I've not checked the most obvious:

Yes, of course I tried filling it with the valve closed, as if I needed to since it was overflowing my kitchen sink, then tried emptying it, filling it(with hot water), emptying it, filling it/emptying it. All with the valve closed then opened to empty.

I had a full tank by the gauge and by water backing up in my sink. Full I think is the most obvious answer here. So, I used my portable dump tank(note-25 gallons) to empty it(completely- 40 gallons) because I wanted to allow it the freedom of gushing from the 4" opening of the gray tank opening on the RV rather than the garden hose that it normally would just in case it was going to dispel something large. I wanted the power of the gush.

So, when I drained it till no more was coming out... it filled but maybe a little more than half of the 25 gallon portable dump tank from my 40 gallon gray tank. Approx 12-15 gallons.

I'm hoping I've convince even the most confident doubter that my 40 gallon gray tank has some issue beyond the gauge being bad, a plugged p trap.

Sorry, I don't mean to be rude but some of the things some suggest must feel I'm not too bright at this despite my being a full time RVer since 2007, near 30k miles on the road most in the rough, and never had issues with black or gray tanks.

cephoto wrote:
ok, for those of you that seem to think I've not checked the most obvious:

Yes, of course I tried filling it with the valve closed, as if I needed to since it was overflowing my kitchen sink, then tried emptying it, filling it(with hot water), emptying it, filling it/emptying it. All with the valve closed then opened to empty.

I had a full tank by the gauge and by water backing up in my sink. Full I think is the most obvious answer here. So, I used my portable dump tank(note-25 gallons) to empty it(completely- 40 gallons) because I wanted to allow it the freedom of gushing from the 4" opening of the gray tank opening on the RV rather than the garden hose that it normally would just in case it was going to dispel something large. I wanted the power of the gush.

So, when I drained it till no more was coming out... it filled but maybe a little more than half of the 25 gallon portable dump tank from my 40 gallon gray tank. Approx 12-15 gallons.

I'm hoping I've convince even the most confident doubter that my 40 gallon gray tank has some issue beyond the gauge being bad, a plugged p trap.

Sorry, I don't mean to be rude but some of the things some suggest must feel I'm not too bright at this despite my being a full time RVer since 2007, near 30k miles on the road most in the rough, and never had issues with black or gray tanks.

Have no doubt you have issues!
Tank Venting OR tank outlet. Either/both are plugged up.

YOU stated that you had tried all the obvious so 'Time To Poke'

So if vent is clear/runs free, has not dropped down into tank......then when are you going to poke?

Simple question.

Bye.

I have heard of the shaft becoming disconnected from the slide valve.

I have been battling gray water issues as well. My symptoms were a bit different but may be relevant.

I also have two gray tanks. One for the galley and the other for the head & laundry.

I keep my black valve closed and my gray valve open.

I have been having trouble with "mystery leaks" from the clothes washer for months. My washer is on the passenger side and the leak showed up as wet carpet on the drivers side storage bay. It took me weeks to figure out that it was coming from the washer. Only occurring when "large" loads of laundry were run.

While trying to figure that out the shower and vanity sink began to back up.

I tried the garden hose and snake methods.

After MUCH profanity and MANY showers I gave up and bought a gallon of Draino drain cleaner.

I know that I am going to get some grief for that but after much study I came to the conclusion that, other than the seals in the drain valve, all of the materials used in the waste plumbing in my 5'er are the same as in my house.

I poured 1/3 gallon in each of the drains (shower, sink and washer) and let is sit for two hours. I followed that with copious amounts of hot water.

Success!!

No more laundry leaks. No more standing in 3" of water while showering. Also, the "crud" that had been building up on the lower 1/3 of the drain pipe where the sewer hose connects is gone.

Good luck with your troubles.

S.