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Grey water tank won't drain completely

epennal
Explorer
Explorer
New RVer here. My Grey water tank will only empty down to the 2/3rd level. Not completely clogged, obviously, but why would it stop draining at that point? I don't think it's a sensor issue because it does seem to stop short of completely emptying, plus it doesn't take long to fill back up to the full mark.
1 ACCEPTED SOLUTION

DOTLDaddy
Nomad
Nomad
This is what I would do if I wanted to check how much water it takes to fill up the grey tank:
  1. Drain grey water tank until no water comes out of sewer outlet
  2. Close grey water valve
  3. Get a bucket with a known fill mark, say 3 gallons
  4. Fill bucket to 3 gallon mark and pour down your shower drain
  5. Repeat as many times as it takes until shower starts to back up
  6. If it took 10 buckets, then you have 30 gallons capacity
  7. If it takes, say, 5 buckets until full, 15 gallons, then ya probably got a problem

I am assuming your grey tank should hold at least 30 gallons, BTW.

Walter & Garland - Camp Canine caretakers
Miss Inga (aka "Shorty") - 10 y.o. old GSD.
Gen. Gretchen - Joined Rainbow Div., June 27, 2017 at age 13
Gen. Missy - Joined Rainbow Div., June 11,2006 at age 12
2018 Montana HC305RL 5th wheel
2018 Silverado HD 6.0L

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20 REPLIES 20

MNtundraRet
Navigator
Navigator

I would find a grease remover at a RV store, or supermarket. Let it sit for a few days and then drive around to loosen thing up. The vent may not be the problem. 

Mark & Jan "Old age & treachery win over youth & enthusiasm"
2003 Fleetwood Jamboree 29

Katdaddy
Explorer II
Explorer II

Sounds like youe sensors are dirty. Buy the cheapest liquid dish washer detergent you can find, before next trip add 5 gallons of hot water and a cup of the detergent. The action of riding down the road will clean the sensors. Also helps if the gray tank starts to smell.

Little by little, one travels far - J.R.R. Tolkien
There ain't no surer way to find out whether you like people or hate them than to travel with them. - Mark Twain

Olcoot
Explorer II
Explorer II

Glad you said you are a New RVer. We gave up trusting the gages years ago. Mostly there as a make you feel good thing. Mine read full after emptying and I knew they were empty. Simplest thing to do with ether gray or black tanks... key word "simplest". Dump 5 to 10 gals of water, half bottle of dawn into each tank. Hookup and drive about 5 miles OR do just before your next trip and at your first over-night dump. And don't be surprised your sensor still reads 2/3rd. The sky is not falling, just cheap sensors. 

Cybergrunt
Nomad
Nomad

Ask around and see if anyone near you has a digital camera inspection camera. If not, cheap models at Harbor Freight go for less than $100. Kind of handy for more than RV use.

2021 Forest River Wildwood Heritage Glen 24RLHL: 810-825# TW, ~7500# GVW
2020 F-250 XLT Super Duty SRW: 7.3 V8 gasser, 3.55, 10spd

bluwtr49
Explorer II
Explorer II
Remember also that if you sensor is acting up it may say full when actually much less. That would make dumping the tank seem faster if you dump when it indicates at or near full.

I would be in favor of a bad sensor first off.
Dick

2002 43' DP Beaver Marquis Emerald Cat C-12 505 HP, 1600 Tq
2003 Jeep Grand Cherokee Overland ---toad

Executive45
Explorer III
Explorer III
1/3 of your grey tank has a big hard mess of grease, hair, dried food and garbage across the bottom of it. You'll need to have the tank removed and replaced. Figure about $3k for the job!...:W

Really, follow DOTLDaddy's suggestions above and you'll know for sure if it's a sensor or something similar to above. Anything else is simply speculation. Filling the tank to capacity is the easiest way to trouble shoot.

If you're a glass half-full half-empty kind of guy, you could reverse the procedure. That is, once your tank if FULL, empty it into buckets and measure how much comes out..:)...Dennis
We can do more than we think we can, but most do less than we think we do
Dennis and Debi Fourteen Years Full Timing
Monaco Executive M-45PBQ Quad Slide
525HP Cummins ISM 6 Spd Allison
2014 Chevrolet Equinox LTZ W/ ReadyBrute
CLICK HERE TO VIEW OUR TRAVEL BLOG

And the tank monster will form from the mass and take over the earth...no, you aren't going to fill 1/3 of your grey tank with grease and hair. Even 1 inch on the bottom would be a lot. 

As others have suggested, filling with a measured quantity of water after dumping will tell you if it's empty or not.

Tammy & Mike
Ford F250 V10
2021 Gray Wolf
Gemini Catamaran 34'
Full Time spliting time between boat and RV

rgatijnet1
Explorer III
Explorer III
A plumbing snake run up through the drain valve should move any obstruction out of the way. It might not get it out of the tank but it would let you know if there is an obstruction.

From the bottom going out to the sewer or from the top through the vent on the roof?

Old-Biscuit
Explorer III
Explorer III
epennal wrote:
New RVer here. My Grey water tank will only empty down to the 2/3rd level. Not completely clogged, obviously, but why would it stop draining at that point? I don't think it's a sensor issue because it does seem to stop short of completely emptying, plus it doesn't take long to fill back up to the full mark.



New RVr........IS this a NEW RV also?

2 possibilities:

A) Dirty sensor. As suggested empty grey tank then when it has completely stop running any water out....run water quickly down into grey and watch for increased draining.

B) NEW RV......workman didn't retrieve the 'cut-out' disc from when they cut drain/vent/dump line holes into tank.
Disc floats around until you dump.gets pulled down to drain hole and blocks it off. Then drain valve closed and disc floats again until next time.

When grey tank stops draining....close drain valve, wait a few minutes, rock RV to slosh grey tank then open drain valve...does it start/stop flowing again??

Cut-out disc left behind....NEW RV.........DEALERS PROBLEM cause you will have to disconnect drain line/drain valve and hand fish for cut-out disc.
Is it time for your medication or mine?


2007 DODGE 3500 QC SRW 5.9L CTD In-Bed 'quiet gen'
2007 HitchHiker II 32.5 UKTG 2000W Xantex Inverter
US NAVY------USS Decatur DDG31

rgatijnet1
Explorer III
Explorer III
epennal wrote:
Thanks for the quick replies, everyone. I'm never sure of anything, when it comes to the tank senors. Lol
My impression is, it takes less time to drain than it used to. It's like, "Wow. Done already?" That, plus it only takes a day to reach Full again (normal water usage), rather than the 3 days it used to take, after emptying the tank. It's a 52 gallon tank. Just doesn't make sense.
I've left the valve open for several days, and it never goes below 2/3rds full. It doesn't go back to full until I close the valve. I'm hoping the next time we drive it, maybe something will work itself loose and the problem will go away.


I have heard of a piece of plastic, left when they cut the hole in the tank for plumbing, was blocking the drain valve. If that was the case, I doubt that you would get anything to drain from the tank, or it would drain very slow, but still empty completely.

epennal
Explorer
Explorer
Thanks for the quick replies, everyone. I'm never sure of anything, when it comes to the tank senors. Lol
My impression is, it takes less time to drain than it used to. It's like, "Wow. Done already?" That, plus it only takes a day to reach Full again (normal water usage), rather than the 3 days it used to take, after emptying the tank. It's a 52 gallon tank. Just doesn't make sense.
I've left the valve open for several days, and it never goes below 2/3rds full. It doesn't go back to full until I close the valve. I'm hoping the next time we drive it, maybe something will work itself loose and the problem will go away.

So what happened when you tried to fill using a bucket to measure? 

If you left it open for 3 days, even if partially blocked, any water should have been able to dribble out if it was a partial blockage. 

Tammy & Mike
Ford F250 V10
2021 Gray Wolf
Gemini Catamaran 34'
Full Time spliting time between boat and RV

DOTLDaddy
Nomad
Nomad
This is what I would do if I wanted to check how much water it takes to fill up the grey tank:
  1. Drain grey water tank until no water comes out of sewer outlet
  2. Close grey water valve
  3. Get a bucket with a known fill mark, say 3 gallons
  4. Fill bucket to 3 gallon mark and pour down your shower drain
  5. Repeat as many times as it takes until shower starts to back up
  6. If it took 10 buckets, then you have 30 gallons capacity
  7. If it takes, say, 5 buckets until full, 15 gallons, then ya probably got a problem

I am assuming your grey tank should hold at least 30 gallons, BTW.

Walter & Garland - Camp Canine caretakers
Miss Inga (aka "Shorty") - 10 y.o. old GSD.
Gen. Gretchen - Joined Rainbow Div., June 27, 2017 at age 13
Gen. Missy - Joined Rainbow Div., June 11,2006 at age 12
2018 Montana HC305RL 5th wheel
2018 Silverado HD 6.0L