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Old 05-11-2016, 12:00 PM   #15
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Location: Eastern, PA
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Originally Posted by BFlinn181 View Post
The black and grey tanks usually have a roof top vent, some may be joined to only one vent, but not usual, I think. It looks like this:
CAMCO RV 40032 - Camco RV Plumbing Vent, 2-1/2", Polar White 40032 - RV Plus

If the vent were blocked, putting water in the tank or emptying it would cause the tank to 'oil can' before pressure would build up and cause a leak out the AAV. I'd really look for a loose or leaking fitting or split line from the tank flush connection.
Thanks BFlinn181 you have been a great help!

I'll post my findings back on this thread on exactly what the cause\fix was.

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Old 05-23-2016, 04:06 PM   #16
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Location: Eastern, PA
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Found the problem!
The black flush connection was indeed leaking. The black flush line runs under the bathroom sink has a check valve or vent (it's an odd piece) on top then goes down into the black tank. The threaded male connection from the actual flush connection had no thread tap on it. Put some thread tape on it screwed in the female end and no water...however it is dipping a little bit, so we are going to have the dealer look at it.. it's simple plumbing, but better be safe then sorry. The awning is now giving us an issue..one end will not stay up, appears to be the plunger is bad, so it has to go back anyways!

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Old 05-23-2016, 04:25 PM   #17
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Glad you found the problem. Mel S and I were both mistaken, the vacuum breaker in the flush line is different than an AAV. However, the advice to eliminate it is still wrong. It's there to prevent water in the flush line from draining back into the hose or even the water line the hose is attached to. In a worst case situation, if you disconnect the hose from the hydrant while full of water to the tank sprayer, contaminated water could drain all the way into your hose. Next time you hook up hose, everyone in your RV could be sickened, which would really give your black tank an exercise!

Things required by code shouldn't be eliminated, the code was written for many reasons other than to make plumbers rich.

Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI
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Old 05-24-2016, 07:19 AM   #18
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Originally Posted by lynnmor View Post
You are talking about oranges, I was talking about apples. If you would have clicked on the link, you would have seen the parts that make up a flusher.

On the 4th page it says this:

Make sure faucet is open completely during entire tank flush cycle. Vac/Check is designed to work at water
pressure range of 8 125 psi. Water leakage from Vac/Check is likely when water pressure in supply line is
under 8 psi. It is normal for a small amount of water to escape Vac/Check as plumbing line for tank flush
I you are correct... (we where talking about apples and oranges).
My mistake.

When the OP said "there is a vent under the sink" I assumed he meant the "Air Admittance Valve, (AAV)", in the sink drain system.

However because he has water leaking from what he calls a "vent" when he's running pressurized water into the black tank flusher....what most likely is leaking is the "vacuum breaker" in the fresh water line going to the black tank flusher:


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Old 09-06-2016, 06:35 PM   #19
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This is my first post on the forum. I am a newbie TT user and I had this same problem. Made the mistake of closing the black dump valve while using the flush system. A few hours after leaving the campground we smelled strong sewer odors in the bathroom. When camping at another site that evening I smelled it again at the other end of the trailer when opening the entry door. Called our dealer's service people and they had no clue. I am going out to the trailer tomorrow to open the bathroom cabinet and see if I can find the vacuum breaker device and determine the extent of the spill/damage. The attached information above indicates the device should not be installed inside due to frequent releases. So obviously it HAS TO GO. I am thinking about replacing it with a simple check valve. Anyone see any problems with that?

Thanks to Lynnmor for identifying the problem and linking the information.
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Old 09-06-2016, 07:01 PM   #20
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You will find a check valve in mine and no vacuum breaker. Your water inlet may already have a check valve in it, if not, replace it with one made for a city water inlet.
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Old 09-07-2016, 05:53 AM   #21
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Most likely the check valve. We took ours back to the dealership to get fixed and that is what it was. Just couldn't believe a bad check valve caused the issue. I am the OP for this topic/question
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Old 09-07-2016, 11:45 AM   #22
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I went out to the trailer and looked around. I found the vacuum breaker/vent right up under the bathroom sink. It is the small black elbow on top of the two white hoses, but it looks like the photo is upside down (sorry). There was a small spring loaded button on top that must be the vacuum breaker/vent. Fortunately, there was no evidence of liquid spillage in the cabinet. So it appears that during flushing, if the black water dump valve is accidentally closed, then the tank pressurizes and burbs a big glob of sewer gas out of the vent. This would suggest that there is no roof mounted vent for the black water tank. I find that very strange. I will have to get up on the roof and check that out. I still think I will replace the vacuum breaker/vent with a normal check valve to prevent future problems. Thanks all.
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Old 09-07-2016, 12:24 PM   #23
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RV MFG.s are 'required' to install those anti-siphon vacuum breaker devices on black tank flush system due to POSSIBLE cross contamination of waste water with potable water

Possible but NOT very PROBABLE
Possible because potable water source is connected to a system that feeds into a waste water system

NOT PROBABLE due to flush system design and the plain old fact that multiple errors would have to happen (the perfect storm ----possible but highly unlikely)

Flush System

Black tank would have to get FULL....so full that flush nozzle at top of tank is under water-----and then level would have to go up vent pipe far enough to be above the top of anti-siphon vacuum breaker which are high up under bathroom sink cabinets.
Then it would have to flow out hose connection which may or may not have a plunger check valve (like city water connection) and then flow thru potable water supply hose and into water source system which would have to be completely depressurized for water to back flow from RV into Potable Water System.

Possible............just not Probable

Those anti-siphon vacuum breaker devices are OPEN to atmosphere (top cap covers opening) and when internal plug doesn't pop up and seal opening off water sprays into bathroom cabinet----great!

Remove device----replace with couple of 1/2" PVC elbows
Change out flush system hose connection with one that has a check valve (City water inlet type) if yours doesn't have a check valve already
Use a hose end anti-siphon vacuum breaker device like this one

No more water spraying inside RV
No back flow issues

BUT one should use a pressure regulator at water spigot with a 'wye' hose connector.....one side for potable water supply and other side for flush system

Water pressure regulator on flush system..........high pressure can damage spray nozzle. It is just plastic with holes drilled into it.
Besides 50# regulated water pressure is more than adequate

And remember........
Dump when FULL ---high liquid level/volume/weight will carry majority of stuff down and out. Quick flush/rinse is all that is needed to spray down sides and clear bottom of tank.
They are holding tanks and don't need to be spic-n-span clean.
Add a few gallons back in after dumping ----enough to fill dump line and keep bottom of tank wet

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black tank, tank, water

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