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Old 08-19-2016, 10:08 PM   #1
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Black Tank draining issue "help"

To all you smart RVer's - I have a problem and need some of your awesome advice.

Problem - I drain the Black tank in my 5th wheel after camping and return home to park the RV. I go out camping a few weeks later - pull off the cap and black water (or it appears to be) comes out of the drain line. It's not a spoon full or a cup full, it's more like a bucket full. The valve is closed ofcourse and I can't figure out how this happens. I ensure the tank is fully drained and the black tank valve closed before opening the grey water valve. Help me out folks.

Thanks in advance


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Old 08-19-2016, 10:35 PM   #2
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Unless you can tilt your trailer so the black tank drain will be low you won't be able to get everything out. It sounds like your black tank drain valve is leaking and you can either replace it or try to clean it. Some paper may have gotten stuck in it and lets it leak. You can get one of these to insure that when you take the cap off nothing will come out.

Twist On Waste Valve, 3 - $18.65

My black tank valve was getting hard to operate so I bought one just in case. You may be able to find one cheaper, I just used this one for an example.


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Old 08-19-2016, 11:42 PM   #3
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Welcome to the forum,
Sorry to hear that.
X2 ^^^ my thoughts as well. It's difficult to know where the drain line exits the holding tanks. Are you sure no one ran anything down any drains in that length of time? Don't forget to empty the bowl before travel too.
We use the "valve" as well while parked, but we don't travel with it on.
I'd perhaps use one of these if this has happened a second time.
Walmart usually has them.

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Old 08-20-2016, 06:17 AM   #4
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Is it possible that the 3" sewer line runs a little uphill from the tank to the cap? I have seen dump stations where the road slopes away from the drain. If either of these occur, you could have stuff left in the low spot of your pipe that then runs out the next time you open the cap. Other than that, there could be small "stuff" in the edges of your valve that don't let it fully close, how does it feel when you close it? Another thing I do when dumping is that I leave the black valve open when dumping grey so a little bit washes back and helps clean out that black pipe. Depending on your parking situation, can you run some fresh water into the black tank after dumping that will 'slosh' around as you drive, then find a place to dump it when you get home or close to home?
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Old 08-20-2016, 03:55 PM   #5
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I agree the black valve is probably leaking, the tank isn't fully empty, and motion on the return trip is further emptying the tank. Check it as soon as you get home with the valve closed, then open it. In total you will probably get that bucket full.
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Old 08-20-2016, 07:44 PM   #6
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Yep, been there, done that.....it's leaking at the seal. Easy to replace once you thoroughly drain and flush it.
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Old 08-21-2016, 12:02 AM   #7
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Sometimes its hard to verify that the black water tank valve closes and seals... I've had issues with mine.... so I installed another valve where the outlet cap is located... so that when I pull the cap, there is not a bucket of stuff that rolls out....

I also use a clear plastic elbow on my hose so that when I dump/flush the tanks I know that when the water runs clear its safe to close the valves...

We always try to than fill the toilet 3 times and add a cup of either washing machine soap or oxy-clean.... its our thought that as we drive down the road... the water will mix with the soap and wash the inside of the tank...
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Old 08-21-2016, 09:47 AM   #8
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Agree that there is either something in the valve that is preventing it from sealing completely or the black valve us leaking. It is not really the best idea (IMHO/research - others may have their own opinion) to leave the black tanks empty/dry. Once I dump the blank tank, flush/rinse, and close the valve, I always set it up for the next outing/trip with Camp Kem and at least a gallon of water. This prevents future smells and helps digest anything that didn't come out and might still be in the tank. 17 years and no blank tank issues. Good luck on an easy repair should your valve be leaking...happy camping!
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Old 08-21-2016, 09:54 AM   #9
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It's either a bad valve or something wedged in the valve body preventing it from fully closing. Either way, the valve will have to be pulled out for replacement or repair.
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Old 08-22-2016, 07:43 PM   #10
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Thank You all very much. I ended up ordering the twist on valve that was recommended and as a interim fix. I'll have the valve fixed upon return from vacation because based on your advice I believe the valve is leaking. I towed the 5th wheel last weekend and just to verify the leak I got a bucket and twisted off the cap and it had black water that came out (valve closed). Also, I learned from you all to add water and possibly some tank treatment after draining the black tank, so thanks for that lesson, I didn't know that I was supposed to do that. Thanks again everyone.....I always get quick replies that help.

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Old 08-24-2016, 09:19 AM   #11
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Not sure if you do this or not, but try opening and closing the valve numerous times while dumping. It may dislodge whatever is in your valve. You can also backflush your tank with an adapter on the outlet and do the same thing...opening and closing the valve. Either way will also "slosh" the contents of the tank, moving some of the more solid material around.
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Old 08-27-2016, 09:55 PM   #12
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Mike, I think you made a wise choice in getting a twist on valve. I have one that I keep on my 5th wheel at all times but, for the same and different reasons. If I'm at a dump station that I cannot hook up my tank wash, I will close it after I empty my black tank, but keep the black tank valve open then open one of my grey tanks and back flush into black tank for about I don't know 15-30 seconds I'm guessing, I just turn it off before my small grey tank is empty. I shut off grey valve open twist on valve and drain black water again. The main reason I have it is so when I'm dry camping I can equalize my 2 grey tanks and have 82 gallons of grey water capacity for kitchen and bath. But I have had I'm thinking toilet paper stick in the black valve and not seal all the way, this way I don't get a surprise when I take the cap off. Just my 2 cents worth.

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