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Old 09-26-2019, 08:18 AM   #1
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Vacuum Breaker B&B Model 571

I had a leak under the bathroom sink where my vacuum breaker B&B model 571 is. So I thought it would be an easy fix to replace it with a new one. After a couple of days, it started leaking again.
I asked the RV dealer why it would be leaking and he said, there must be something wrong with my fresh water system as there shouldn't be any pressure in that vacuum breaker line. The vacuum breaker is only to stop the black water from syphoning back into the fresh water system. So I drained the supply hoses going to the black water flush and it seemed to be ok until I used the black water flush again. So I drained those lines again, but now on my last trip, I am getting a leak from that vacuum breaker again even though I haven't used the black water flush. Any idea what is going on there?
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Old 09-26-2019, 08:35 AM   #2
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The plastic B&B vacuum breakers are prone to leaking very quickly. Ours leaked on the 3rd or 4th trip. The best thing to do is to get rid of it and replace it with something better. You have a couple of options for replacing it.

You can buy a Watts 288A brass vacuum breaker valve or use a hose bib type vacuum breaker valve on the hose line externally. If you opt for the less expensive hose bib style valve you’ll need a 90 degree elbow fitting inside to replace the B&B junk.
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Old 09-26-2019, 09:29 AM   #3
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First... the vacuum breaker for the black tank flush IS NOT connected in any way to the fresh water tank or the fresh water system INSIDE the R/V. I have no clue why the dealer told you something like that? It is only ever connected to the spigot's fresh water supply when you connect a hose between the spigot and the black tank flush connection, hence the need then for a check/anti-siphon/vacuum breaker. If the spigot's water pressure would suddenly drop AND create a siphon AND the black tank was full it could POSSIBLY suck black water into the spigot and the supply. That's a LOT of IFs and ANDS but none the less a check/anti-siphon/vacuum breaker is required by law should that happen.

Second... when you say you drained the supply hoses for the for the black tank flush and it cured your problem temporarily, you lost me. Do you leave your black tank flush hose (there is only one so I'm not sure why you said hoses) connected all the time? If you do, then the residual water in the black tank plumbing cannot run out (and you will notice it does when you remove the supply hose at the black tank flush connection) and water stays trapped in the plumbing and the check/anti-siphon/vacuum breaker valve. While there is no pressure on the black tank flush plumbing at that point, if you trap water in there, it is a possibility it could leak out of the valve if it is defective.

Finally, I have read where many of the black plastic valves have failed.
Most replace them with the brass Watts valve recommended by itat.
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Old 09-26-2019, 10:53 AM   #4
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Quote:
Originally Posted by 5picker View Post
First... the vacuum breaker for the black tank flush IS NOT connected in any way to the fresh water tank or the fresh water system INSIDE the R/V. I have no clue why the dealer told you something like that? It is only ever connected to the spigot's fresh water supply when you connect a hose between the spigot and the black tank flush connection, hence the need then for a check/anti-siphon/vacuum breaker. If the spigot's water pressure would suddenly drop AND create a siphon AND the black tank was full it could POSSIBLY suck black water into the spigot and the supply. That's a LOT of IFs and ANDS but none the less a check/anti-siphon/vacuum breaker is required by law should that happen.

Second... when you say you drained the supply hoses for the for the black tank flush and it cured your problem temporarily, you lost me. Do you leave your black tank flush hose (there is only one so I'm not sure why you said hoses) connected all the time? If you do, then the residual water in the black tank plumbing cannot run out (and you will notice it does when you remove the supply hose at the black tank flush connection) and water stays trapped in the plumbing and the check/anti-siphon/vacuum breaker valve. While there is no pressure on the black tank flush plumbing at that point, if you trap water in there, it is a possibility it could leak out of the valve if it is defective.

Finally, I have read where many of the black plastic valves have failed.
Most replace them with the brass Watts valve recommended by itat.

And why is the black tank fresh water flush anti-siphon located under the sink? Their basic design has "holes" in it to relieve the pressure and there's no place for it to go except on the floor. Something's fishy here me thinks.
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Old 09-26-2019, 11:00 AM   #5
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And why is the black tank fresh water flush anti-siphon located under the sink? Their basic design has "holes" in it to relieve the pressure and there's no place for it to go except on the floor. Something's fishy here me thinks.
Nothing fishy at all. Plumbing code dictates the the valve has to be mounted higher than the toilet. So they typically mount it under the bathroom vanity up under the counter which should always be higher that the rim of the toilet.
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Old 09-26-2019, 11:28 AM   #6
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Originally Posted by nayther View Post
And why is the black tank fresh water flush anti-siphon located under the sink? Their basic design has "holes" in it to relieve the pressure and there's no place for it to go except on the floor. Something's fishy here me thinks.
This may help. Doesn't matter where it's located just so it's at least 6" above the highest use item (toilet rim). Mine is 5 feet above in the washer/dryer provision cabinet. funny how this issue goes on and on and on. If the valve is functioning properly and the tank end is open there is no pressure within it.
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