Flushing Tank Question

[Willis]

Originally Posted by Rongrice

Has anyone else had a problem with the tank flush just backing up with pressure? Mine seems to be blocked with something, can only imagine what, and am not sure how to clean it.
Does anyone have any good suggestions of what to use to clean out the tanks?
Ron

I hate to say this and there are some other threads around here somewhere on this problem, but some people have reported in the past on such blockage problems on brand-new units.

After jumping through all the hoops it sometimes came to the point where the tank had to be completely disconnected and dropped to find the problem. I remember one poster who said that when the hole for the toilet was drilled out that the "disc" of plywood had dropped into the tank. It was probably close to quitting time and the worker who made that mistake conveniently forgot to fish the piece out of the tank. Well, that piece of wood blocked the drain and the whole tank wound up full of sludge and it was a nightmare of a mess.

I REALLY hope that isn't your problem, but on a brand new unit you should not have enough of a build-up to cause an almost complete blockage. The only way that might happen in normal usage is if you kept the valve open all the time. That's a no-no...you need to have a good amount of liquid in the tank at all times until it is drained. (And personally, I always add several gallons of water afterwards when the TT is not in use.)

[ronhanson]

There is a check valve in the black tank flush line which can go bad that blocks incoming water. The are usually located inside in a cabinet behind a false wall.

[herk7769]

First of all this is not a problem; it is a feature.

It means your check valve is doing its job.

The check valve is located higher than the fill port in order to form an anti-siphon air block. It prevents water from the black tank from entering the hose you are flushing with and also prevents siphoning black water out of the tank when full.

When you flush the tank, water under pressure fills the hose all the way to the black tank. When you turn off the water, the check valve closes and the water trapped in the hose from the fill port to the check valve has no place to go, but back out the way it came in.

When you disconnect your flush hose, that water (under pressure from the faucet) gushes out. There is not much water (about 1-2 quarts) but it looks like a lot since it is under pressure.

[ronhanson]

Some check valves will stick closed and not allow water back in from the hose when you reconnect to flush the tank the next time. The tank flush line then appears plugged and wont flush at all. This happened to mine and I needed to replace the check valve.

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Black Tank Flush Plugged