Black water tank pressure build up

jpdoggett

Well-known member
I have a 2011 Landmark Augusta this not my first fifth wheel, but when I flush the black water tank it builds up pressure in the tank, this is with the drain valve closed, and when we are using the stool it will build up pressure and blow back into the stool, you never know what the level is cause the tank always says it full. Dealer says there is nothing wrong with it that you are to flush the tank with the valve open, and he says I am waiting to long to dump. I have never had this problem with any other brand of RV
 

boatto5er

Founding VA Chap Ldr (Ret)
I have a 2011 Landmark Augusta this not my first fifth wheel, but when I flush the black water tank it builds up pressure in the tank, this is with the drain valve closed, and when we are using the stool it will build up pressure and blow back into the stool, you never know what the level is cause the tank always says it full. Dealer says there is nothing wrong with it that you are to flush the tank with the valve open, and he says I am waiting to long to dump. I have never had this problem with any other brand of RV

Your dealer is full of the stuff in the tank!:rolleyes:
 

JohnDar

Prolifically Gabby Member
Sounds like a dealer that should be selling used cars. If the vent is obstructed, then the gases from the decomposing waste are going to build up in the tank and get released when you flush the toilet.

If you always flushed with the drain valve open, you'd end up with a pile of nasty at the bottom of the toilet drain pipe. TP and excrement need water in the tank to break up and decompose.
 

Birchwood

Well-known member
We had the blow back a couple times but eventually it goes away.Its an air lock that means the vent may be clogged with paper and crud.
Just keep filling the tank with water and flushing .
 

Rickhansen

Well-known member
The owners manual say to only flush the black tank with the dump valve OPEN. I believe the roof vent is connected to the side of the tank, hence the "burp" you get when flushing the potty when the tank is nearing full. If you suspect a plugged vent line I'd suggest removing the roof vent cap for the black tank, and flushing the vent line with a garden hose. It will clear any obstruction and prove that the vent line is unobstructed.
 

Willym

Well-known member
Well someone connected our water supply hose to the flusher connection in error while on our way home from Texas this past winter. It wasn't long before air bubbles started appearing in the WC. While scratching my head on this situation we had a vent "emission". Fortunately the tank was pretty clean so not too much mess. It also pushed the WC off the floor a little. The power of hydrostatic pressure times surface area! I'll always do the water hook up in future...
I have always flushed my tank with the black valve open, and never had any tank "build ups". My event was reinforcement for this. The tank fills quickly, and if you get distracted in the process, bad things can happen.
 

slaytop

Well-known member
Just a thought. Check to see if the black vent pipe is too long and is tight against the vent cap on the roof. If so, that would seal the end of the pipe and not let it breath.
 

jpdoggett

Well-known member
Thanks to all of you for your help and comments. The dealer told me they check the vent to make sure it was not plugged. The RV is in Texas so when I get back to Texas in Oct will do some checking om my own. and again thanks
 

sunflower

Active Member
If you flush with the valve closed all you are doing is filling the tank,you can do that from the inside with the toilet.The best way is to make sure the tank is at least 3/4 full and have the flush hose on then pull the valve creating a strong flushing action,leave the flush hose run until clear discharge is evident,with the valve OPEN.While flushing dropping a bowl or two full of water will also help prevent a mound.
 

JohnDar

Prolifically Gabby Member
My bad. I misread the original post. If he was getting back pressure releasing when flushing the commode, then definitely the vent was blocked. When using the tank flush at the UDC, then the drain should be open.
 
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