Black Tank Flush

[KC's]

If I use a Y connector for our freshwater and black tank flush, is there a chance there could be a backflow from the black tank flush that could contaminate the freshwater side of the Y connector?

[Carl n Susan]

There is an anti-siphon valve in the black water flush system to prevent back flow. But I wouldn't do it as the anti-siphon valve is notorious for failing.

[KC's]

I have put a backflow check valve at the connection going into the flush. Should I feel safe with that?

[MARK A]

Originally Posted by KC's

If I use a Y connector for our freshwater and black tank flush, is there a chance there could be a backflow from the black tank flush that could contaminate the freshwater side of the Y connector?

I would think as long as you don't leave it hooked up it would be no different than unhooking your drinking water hose putting on your flush hose on flushing, then re-attaching the drinking water hose. If you leave it hooked up, there's a static pressure path for germs.


Mark

[mhs4771]

I have one hose that is used only for the Black Tank Flush.
I know the chances of contamination or slim, but why take the chance.
Also had neighbor who had theirs' hooked that way and filled their black tank because the shut off on the Y didn't totally close.

[KC's]

Originally Posted by mhs4771

I have one hose that is used only for the Black Tank Flush.
I know the chances of contamination or slim, but why take the chance.
Also had neighbor who had theirs' hooked that way and filled their black tank because the shut off on the Y didn't totally close.

Never thought about the Y not shutting off all the way..ltham
Nks for that Carl!! I will 9nly connect when 8 flush now.

[KC's]

I do leave it connected but will no longer do that, THANKS Mark.

[KC's]

Wow what was i drinking, sorry for that spelling! Thanks Carl.

[BB_TX]

I leave my flush hose connected via a Y. And here is why.

The only way to get black water back into the hose and back to the fresh water system is if the spray head is submerged in water in the tank, the flush water valve has been opened, and the public water supply suddenly loses pressure. Why is that? When a public water system loses pressure due to water being shutoff, water begins to flow out the lowest points in the water system. That causes a vacuum to be created in the upper parts of the piping. And that vacuum pulls water and air into the piping. And it can cause water to be sucked out of your home, or RV, system, if you open a valve or faucet. It can even pull some water from your home water heater. That is why when water pressure is restored, you get air blowing out the faucet until the system fills back up with water. And that vacuum is why any water source connected to any system that may pull dirty water back into the public line requires an anti siphon valve. Lawn sprinkler systems is a prime example of one requiring such an anti siphon valve since it may well be in operation during a pressure loss. Outside faucets also since a connected hose may be laying on the ground in a puddle of water.

Now having said that. If you disconnect your fresh water hose from the faucet and connect your flush hose to that same faucet, and the above scenario occurs, water could be sucked back into the faucet and fresh water piping. No different than if you were using a Y. So, it is not the Y that is the concern. It is the fact of the possibility of getting dirty water back past the faucet into the supply. As long as the system is pressurized, there is no possible way for black water to overcome that pressure and find its way back into the system. And a water system does not go from pressurized to a vacuum instantly. It is gradual as water drains out and the pressure drops off.

I eliminated my internal anti siphon valve and use an external anti siphon valve. Even without that valve the likely hood of contamination is remote at best due to the specific situation required for back flow. For one thing, it is certainly not common to start the flush while the black tank is still full. If you drain the tank first, then start the flush, the spray head is not submerged in black water. Secondly, if you know you do not have water pressure, it is highly unlikely you would even consider opening the flush valve. Thirdly, since I am always right there when flushing, I would know if pressure dropped.

I use good quality Y's for the RV and at home and have never had one that did not shut off properly.
But, to each their own.

[KC's]

Wow great article....that all makes sense BB. THANKS for the great info!!

[bcrvman]

Originally Posted by KC's

If I use a Y connector for our freshwater and black tank flush, is there a chance there could be a backflow from the black tank flush that could contaminate the freshwater side of the Y connector?

I run the shower hose to a mechanical water timer to an anti-siphon to the black flush port that goes to the built in anti-siphon. In order to have a problem, two anti siphon's have to fail, and the sprayer head has to be submerged. I am not worried but I will replace that built in cheap plastic anti siphon shortly.

[Cat320]

Originally Posted by mhs4771

...I know the chances of contamination or slim, but why take the chance....

That's the bottom line.

[jcurryii]

Back flow preventer.
Litorange 2 Pack Brass 3/4" Inch GHT Hose Bibb Connector Backflow Preventer Vacuum Breaker
Amazon's
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$14.99

[bcrvman]

I use 2 anti-siphon connectors and a garden water timer mechanical type. I also set an alarm on my phone and/or watch.
HOWEVER, the odds of the mechanical timer failing while low are not zero, I will add a inline shut off valve as well. If two devices fail then god must just hate me and there is nothing I can do about that.