Black Tank Flush Question

[SabreDoc]

Just wondering if this sounds like a problem or is normal:
After flushing the black tank on my Sabre 35QSIK until the outflow is clear, upon removing the hose from the black tank flush nozzle I notice some back-flow of water from the connection. Not a lot, maybe 1-2 cups worth. It appears clear and has no odor to it. When flushing there appears to be a nominal flow of water from the sewer connection (visually verified through a clear tank extender fitting) and the tank reads empty when I finish. Is this just normal back-flow pressure created by the tank nozzle or is this abnormal and indicates a flow problem?
Thanks,
Doc

[JDWeir]

If I understand what you are saying, mine does this also. Don't think it is a problem as I seem to recall someone here saying that there is a backflow preventer in the line and this is water draining back on the hose side of the backflow preventer.

Jim

[SabreDoc]

Originally Posted by JDWeir

I seem to recall someone here saying that there is a backflow preventer in the line and this is water draining back on the hose side of the backflow preventer.

Hey Jim,
So there is a back-flow preventer already installed in the line between the flush nozzle and the black tank? That's good to know as I was thinking I would need an external one attached to my hose to prevent contamination.
Thanks,
Doc

[JDWeir]

I think there is a back flow preventer, hopefully someone here can verify that.

[JDWeir]

Just crawled into the basement to look. The hose from the black tank rinse connection runs up out of sight then straight back down towards the black tank. I am thinking that it goes up to a back flow preventer.

HTH

[SargeW]

On my Columbus 320RS the black tank flush line runs up through the basement storage roof then goes up to a back flow preventer in the line that is behind the shower valve. Then it goes back down the way it came to the black tank where it is drilled in to the tank just above the black tank drain fitting.

So yes, the flush line will contain a bit of fresh water that will come out when you remove the hose. Unless that is, you put a shut off valve on the line to control the excess water while dumping.

[SabreDoc]

Thanks Sarge and JD!
Appreciate the help.
Doc

[mjones12]

Originally Posted by SabreDoc

Hey Jim,
So there is a back-flow preventer already installed in the line between the flush nozzle and the black tank? That's good to know as I was thinking I would need an external one attached to my hose to prevent contamination.
Thanks,
Doc

I don't know, but I have just assumed there would be one. But just in case, I got a small brass backflow preventer from Lowe's for a few bucks, and I use it externally.

[Herk7769]

I have a short black hose with two back flow preventer (one one each end) and a shutoff valve that I use for turbo flushing the tanks.

It is overkill since there is one at the tank, but why take any chances?

[jeeplj8]

When I recently replaced my water pump I was looking at the black tank flush line as it enters the camper. There is a back flow preventer mounted about 36 inches from the inlet on the side of the camper. This makes it easily accessible inside the cabinet where the water pumo is (which the thoughtfully mounted on top of the main power cord...)

It is also secured above the inlet. In other words, it looks to be designed to allow water in the line between the inlet and preventer to flow out the inlet.

[jevanb]

Mine is installed in the wall next to the master John.. sure makes LOT of noise

[garbonz]

My backflow preventer which is under the bedroom sink is REALLY noisy when I am flushing the tank. Anyone else experience this?. Sounds like the valve is fluttering somehow.

[bubbles]

Yes, typically, the backflow preventers are noisy and not an issue.