My Motorhomes Grey Water Is Dumping Into My Black Water Tank, What's The Problem?

by Perry
(Barto, PA)

I have a 1996 Minnie Winnie. I just took notice that when I went to dump my holding tanks, there wasn't any water flowing out of my gray tank. I thought that was odd, knowing that we used the sink quite a bit on our trip. I then took a 5 gallon bucket of water and dumped it down the sink and I could see the water flowing in the black tank by looking through the toilet opening. Sure enough, when I went to dump the gray tank, there was nothing, and then I opened the valve for the black tank, the water flowed out.

What is happening, and how do I fix it?

ANSWER: Greetings Perry thanks for submitting your question on our Ask An RV Question Page.

There is a possibility that you may not have a problem at all, but there are a couple of steps you need to take to determine if you really have a problem.

On occasion some RV manufacturers have designed their plumbing systems to allow grey water from a bathroom sink, shower or even kitchen sink to go to the Black Water Tank instead of the Grey Water Tank. The simple reason was because the Black Water Tank was closer to the sink or shower then the Grey Water Tank was.

I cannot tell you for sure if your Minnie Winnie was setup that way or not. But there are some steps you can take to find out for sure.

1. Since you did not tell me which sink you dumped the water in, you are going to have to dump water into the other sink and shower to see if they also end up in the Black Water Tank. If all of your sinks and shower all end up

in the Black Water Tank, then you have a problem.

If only one of your sinks or only the shower drain into the Black Water tank and the other sink or shower drain into the Grey Water Tank then it means that the one Grey Water drain that is draining into the Black Water Tank in all likelihood is designed to do that.

2. While you are dumping the water into your drains have someone look underneath the RV to see if any of the water is going onto the ground. If you see water leaking onto the ground, it means that you could have a cracked Grey Water Holding Tank or a leak in a connection to the Grey Water Holding Tank.

3. After you have dumped all of the water in all of your drains, check the Grey Water Tank to see if it now has water in it.

If it turns out that all drains are draining into the Black Water Tank then you have a problem somewhere in your RV's plumbing system. At that point it would be a good idea to take your motorhome in and have it looked at. Once the problem is looked at and diagnosed, you will be able to determine if it is something you want to attempt to repair.

Yes, it will cost some money to have it looked at, but without seeing the problem for myself, I could not even take a guess on what to do to fix it.

Hopefully some of this information has been helpful to you

Do you have any suggestions or comments on this topic? You can add them to this page by clicking on the "Click Here To Post Comments" link located near the bottom of this page.

Happy RVing

RVing Al

Comments for My Motorhomes Grey Water Is Dumping Into My Black Water Tank, What's The Problem?

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Just the opposite
by: Tracy

I have a older 1990 Tioga with a blackwater tank right under the toilet and the grey water tank away from about 7 feet they have nothing I can see that ties them together there drain pipes do end up at the same place both have there own gate valves then go to one outlet right after the gate valves now the question is how am I getting blackwater im the grey water tank I'm typing this on a little phone I hope you can read this and let me know how this is happening

Thanks have an awesome day

grey water dumping into black tank
by: Lola

Thank you all SO much!!!!!!

I have a 2015 Minnie Winnie and have had problems with the grey water draining. I snaked the grey water drain and found a large amount of hair clogging it. It drained wonderful after removing the hair. Went to fill the grey tank from the sink in the Lav and filled up the black tank. I will check the other sink / shower drains and keep my fingers crossed.

Grey Water Is Dumping Into My Black Water Tank
by: Frog

Mine is doing the same thing, but its the first time its done this, before it always worked right.

Gray water going into black tank
by: Chris

I have a 1999 Ford Conquest 23ft. The lav sink dumps into the black water tank and everything else dumps in the gray tank. What I did was put a J Valve which now goes to which tank I want it too. I like the lav sink to go to the black water tank for flushing only. I did a retrofit for my own liking.

Grey water to black water tank
by: Brad Green

We had a 94 brave where the lav sink emptied to the black water tank. We now have a 2010 Sunova whereonly the toilet empties into the black water tank. I would like the lav sink to empty into the black water tank to increase capacity for the kitchen and shower grey water. Is this possible? And safe?

sink to black water
by: Bruce Stone

In 1996 Minnie Winnie the bathroom sink flowed into the black water tank if my memory serves me correctly.

From RVing Al Thanks Bruce, I think that's what is happening here, but you never know that is why I gave him the additional steps, just to make sure nothing else has gone awry with his plumbing.

Happy RVing

RVing Al

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