Black Water backing up in shower when driving.

BKLaw wrote:

Deb and Ed M wrote:
Just a thought: was the ceiling vent open? I wonder if a slightly-open vent created a suction in the bathroom as you went down the road?? Might explain how the sink could have black fluid, without having the whole bathroom afloat in it? Or maybe the vent stack is creating pressure in the tank?

I know in our previous Class C, having the skylight vents open on the roof created enough suction, that black-tank odors were drawn into the RV unless we created equal pressure by turning on the dashboard air or opening a window. At least on a Class C, the tanks are farther below the bathroom fixtures (plus we seldom boondocked. The tank was usually empty when we traveled)

Yes it was, the one in the bathroom.... That might have had something to do with it.

It was explained to me, that the curved top of an open vent creates aerodynamic suction/lift; and apparently quite a bit of it! If the bathroom door was closed (surely it was while on the road) - then there's no way for air to get into the bathroom to balance out that vacuum, so in the case of a Class C, the air comes from the black/gray tank vent, back up through the drain pipes, into the room. Of course in a TC, the tank is much closer to the fixtures, so you actually got liquid.

Keep the vent closed, and see if it happens again on your next trip??

Terrick down Under wrote:
Hey, we had a similar problem just after we had bought our TC. When I opened up the lower space next to the shower I found a non return valve just around the corner, about 8 inches from the shower drain and not easy to get at. When I finally got it out I found all sorts of junk stopping the valve from shutting off. Put it back all clean and have not had a problem since.
Hope this helps.

Are you talking about a P-trap, or an actual valve that you can turn on and off?

Deb and Ed M wrote:
Just a thought: was the ceiling vent open? I wonder if a slightly-open vent created a suction in the bathroom as you went down the road?? Might explain how the sink could have black fluid, without having the whole bathroom afloat in it? Or maybe the vent stack is creating pressure in the tank?

I know in our previous Class C, having the skylight vents open on the roof created enough suction, that black-tank odors were drawn into the RV unless we created equal pressure by turning on the dashboard air or opening a window. At least on a Class C, the tanks are farther below the bathroom fixtures (plus we seldom boondocked. The tank was usually empty when we traveled)

Yes it was, the one in the bathroom.... That might have had something to do with it.

Just a thought: was the ceiling vent open? I wonder if a slightly-open vent created a suction in the bathroom as you went down the road?? Might explain how the sink could have black fluid, without having the whole bathroom afloat in it? Or maybe the vent stack is creating pressure in the tank?

I know in our previous Class C, having the skylight vents open on the roof created enough suction, that black-tank odors were drawn into the RV unless we created equal pressure by turning on the dashboard air or opening a window. At least on a Class C, the tanks are farther below the bathroom fixtures (plus we seldom boondocked. The tank was usually empty when we traveled)

Hey, we had a similar problem just after we had bought our TC. When I opened up the lower space next to the shower I found a non return valve just around the corner, about 8 inches from the shower drain and not easy to get at. When I finally got it out I found all sorts of junk stopping the valve from shutting off. Put it back all clean and have not had a problem since.
Hope this helps.

I had to fish out a tank spray nozzle out of waste tank, so i know it is very clean. I don't remember seeing the vent tube, so will have to wait till I clean it out this weekend. Found roof vent this afternoon!.

Easy stuff first: cleanse tank and make sure vent is open! Thx for the added info. Cleanse = Dump a bag of ice from the store in toilet to tank then drive around corners for 10 minutes come home and drain after ice melts some.

It is a 2005 Six-Pac D850. Sorry no pics of the drain, but assure you it only has one tank, and one drain valve.

I added the Make and Model to my signature, but profile has info and pictures in there, unless I have to select something in preference for others to see it?????

This has just happened this one time, the last time we used it. Probably been on 4 or 5 trips total and never happened before. I have only camped once where there was a dump station, so I know I have traveled home at least 3 times from this lake with waste water in tank. Thanks.

How do you know it is only one tank? Show us pics of the tank valve set-up. Run a hose down the vent and wash it out..usually on top of roof...may need to be creative to get a hose past the vent top depending on type and if it can come off. Show us a pic of that too for better suggestions. Has this just started or has it happened all the time since you got it?

Have you done a tank cleansing? BTW, year make and model would help too...just saying! The more info you can supply gives folks a better chance at solving your issue. Fill in your profile always is good! Help is just around the corner.:?

HMS Beagle wrote:
There is something wrong with your plumbing. Water (or effluent) will find its own level in the entire system. To back up in the sink - which is no doubt at least 2 feet higher than the shower - would require the shower to be 2 feet deep in effluent. This would be more than inconvenient.

Both shower and sink should have traps, and the tank should be vented. If the backup you got was a small amount, it is possible that the vent is plugged (birds, wasps, bad construction) and the tank pressurized by a warming day, this could force the material in the traps up into the bowl and shower pan. To see the actual level of the black tank, hold the toilet flush open, on most RV's you will be able to see directly to the surface of the effluent.

I think this was caused by the waste water moving back and forth in the tank while driving. It was probably less than 1/2 full. There aren't any baffles in the tank.
I agree it is a plumbing issue, just not sure how to fix. I have traveled with the tank FULL and this hasn't happened. Maybe I just need to make sure it is full before leaving????