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Old 11-19-2014, 01:13 PM   #15
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While I agree Red is usually HOT, Red can also be used to designate "Danger" and Well, waste water from the black tank is a Bio-Hazard and thus danger

In your water connections area is a inlet marked "Black Tank Flush" or "Tank Flush" or some such, that is the line to the "Bottom" of that device, The line coming off the top goes to the spray head that is inside the black tank.

ON my coach I put a short (1 foot) hose on that fitting since it's a witch to connect to and a quick disconnect on the other end of the hose.. When I unplug I get a bit of backflow, all fresh water, as that thing "Breaks" the vacuum and lets air in the line,

Technically it is NOT a backflow preventer (If you pressurise the black tank it can flow back) but a Vacuum breaker (prevents siphoning)

Works well too.

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Old 11-19-2014, 02:08 PM   #16
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wa is correct. It's a vacuum breaker. A backflow preventer is more of "swing" type check valve, used on a sewer line.

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Old 11-20-2014, 04:29 AM   #17
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Thanks for all the responses!
So where can I get this part at a reasonable price?
Could I bypass it and if so what would be the best way to do this.
If the spray head is clogged would this cause a leak here?

I guess what I am saying is what is the best way to fix it.

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Old 11-20-2014, 05:11 AM   #18
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The spray head being clogged wouldn't cause it to leak. It has a little rubber disc in it that deteriorates over time. It's probably going to be easier to just replace the whole thing, as I doubt you'll be able to find just parts. Most hardware stores should have a new one. If you want to by-pass it, just cut it out, get some shark bite fittings (or crimp fittings, if you have the crimper), bend the tubing around & tie it together.

The actual purpose of the vacuum breaker, in the first place, is to prevent sucking sewer/drain water into the fresh water supply. I am assuming this line is going to the black tank flush "sprayer".
The fresh water supply could possibly get contaminated if you were cleaning the black tank via the hose connection and the water got shut off or a fire hydrant the street was opened. This would cause a suction on the garden hose/hydrant, thereby sucking the water from the black tank. That's the purpose of the vacuum breaker, to cause a break in the vacuum/siphon.

Bypass it till you can get a new one would probably be ok, but I think I'd like to replace it as soon as possible. Especially being where I think it is.
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Old 11-20-2014, 05:35 AM   #19
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We have a 06 Holiday Rambler and that's the spot mine is at also. the white plastic piece on it is a check valve on the output side going to the black tank. Its a vacuum breaker as stated above but also a check valve. Make sure the check valve stays on the output side. I guess I will be replacing mine again this year as we had 16 degree weather night before last and I never thought to blow out the black tank rinse line until today when I read this thread! Thanks to Lancslad who mentioned that! I always learn a lot here.

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