Black Tank Flush

[Madmax07]

We ended our latest camping trip yesterday. I was at the point where I wanted to flush the black tank. I hooked up the water to the sewer flush on the trailer. However, when I turned on the water it wouldn't go into the black tank. The hose was full of water and under pressure but it wouldn't enter the tank. I did notice that there was no (don't know the correct term) pressure release valve?? like there is on the city water inlet. Is there supposed to be one on the sewer flush inlet? If so, I would assume that is my problem. Otherwise does anyone have any other ideas? I still own a the same trailer seen in my profile. Thanks.

[Carl n Susan]

That is the classic sign of a failed anti-siphon valve. It either sticks closed or it leaks water down the sidewall into the storage compartment and then into the coroplast. You got the lucky fail.

The anti-siphon valve is most likely under the bathroom sink. Some models hide it elsewhere (behind the shower wall for example). You can tell it if there are two white Pex lines going up and back to a funky device. You have two choices:

1) buy a new one, preferable brass
2) Cut the lines in the pass through (behind the back wall), join them together using a shark bite fitting, and adding an external anti-siphon valve to the exterior flush connection.

A Search here on "anti-siphon" will provide hours of reading enjoyment.

[Madmax07]

That's very interesting because I did have my underbelly fill with water. This has been an ongoing problem. Last year when it happened I took it to our RV dealer and they found that one of the grey tanks had a crack in it so they replaced it. Before they replaced it I would leave the gray tank valve open and the underbelly would stop dripping water.

After they replaced the tank I took it out and once again the underbelly filled with water. I took it back to the dealership. They connected trailer to city water and left the gray tank valves closed. They told me they could not make it leak.

So on my recent camp trip I connected to city water with gray tank valves closed. Within 3 or 4 days the underbelly was dripping. I then opened the gray tank valve that services the shower and the 2 bathroom sinks and within a few days the dripping stopped. Could the anti-siphon valve be the issue? My anti-siphon valve is under the bathroom sink in the bedroom.

[rohrmann]

The valve is not connected to the grey tank, only to the black tank. The valve is an air gap as well as a back flow check valve to prevent black tank contents from flowing out if the tank and into a fresh water system. https://www.amazon.com/RecPro-Breake...a-901367944989

[Carl n Susan]

Originally Posted by Madmax07

...Could the anti-siphon valve be the issue? My anti-siphon valve is under the bathroom sink in the bedroom.

Only *IF* you ran the black tank flush. If not, and you had water in the belly, you still have a leak somewhere.

[mlh]

I took my anti siphon valve off and hooked the two lines together and haven’t had a problem since.
Lynwood

[RMcNeal]

Same here. Mine failed and started leaking in the first year. I put a backflow preventer on the hose connection eliminated the anti-siphon valve completely. Easy fix.

[Scootsk]

I guess that’s why my basement floor is now gone in the ODS side.

[ToolMan]

I had a problem with the black tank rinse. Turned out the spray head in the tank was plugged. Removed it, cleaned and reassembled the spray head and solved the problem. A few years later the anti siphon valve went bad so I cut the lines to and from it. Reconnected the lines with a shark bite coupling.

[Madmax07]

To continue this story, today I thought I would winterize the trailer. I turned the pump on and ran all the taps to clear the lines of water. I then put antifreeze in all the lines. I wanted to make sure the grey tanks didn't have water in them so I opened the grey tank valve in the convenience center and black tank sludge came out!
Can anyone help me out? Would this have anything to do with my anti-siphon valve not working?
I am baffled and don't know what to do. I still have the leak as discussed above and now this.

[Scootsk]

Not black tank sludge. Gray tanks produce the same rank smell and sludge that you expect from a black tank.

[Carl n Susan]

The black and grey tanks share the same dump plumbing. It is not unusual to have residual black stuff in the plumbing unless you raise the front of the RV a bunch when dumping. That is why an external gate valve is highly recommended.