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Old 08-01-2015, 09:28 AM   #1
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Black tank flush - leak

Ok. Just when I thought I knew just about every thing there was to know about an RV, I found something new. My camper is equipped with a black tank flush like a lot of campers. Like most people, I don't use it very often. Usually there is a line at the pump out or I'm just in a hurry and don't bother with it. I do a pretty intense flush when I winterize.

As anyone that has camped for more than 10 minutes knows that there is an unpleasant smell that can come from the black tank when you flush (especially if you have the super fan running and pulling the gases up).

This weekend I'm camping with a sewer hookup for the first time so I took the opportunity to give it a good flush. I ran the toilet until tank was nearly full, drained it and then I turned on the black tank flush. Since I'm camping with water and sewer, I was just going to let it run for hours and I have the drain open

Well, I noticed water dripping from under the camper. After a little research it would appear that the black tank flush hose comes up under the bathroom sink, 90s into a fitting and then goes back down through the floor to the tank. What the hell is this fitting for?

Only thing I can think is that it's some type of vent but I'm not sure. Luckily it only drips when the flush in going and about 95% of the water ran straight back down the water hoses and then dripped into the plastic tray in my basement so there wasn't much mess or damage.

What the hell is this??
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Old 08-01-2015, 09:40 AM   #2
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That is a vacuum breaker to prevent a cross connection of your black tank water with the potable water.

Google "Black Tank Flush Vacuum Breaker" and find a suitable replacement. Use SharkBite fittings to replace it.

Bruce
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Old 08-01-2015, 09:47 AM   #3
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That is a vacuum breaker to allow air into the tank flush line so you can drain all water during winterization. Do a search for 'vacuum breaker' and read the 50+ threads about same. If you hit a thread about the vacuum breaker in the back of the toilet, skip it and go to the next. You'll find out how some people replaced the contraption (you have a pic so you can get to it unlike others here) and how some people took the whole loop out of their units.
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Old 08-01-2015, 09:47 AM   #4
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I suppose if you wanted, you could just eliminate that vacuum breaker completely and connect both pieces of PEX together. You should use some sort of back flow prevention at your potable water source, though.

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Old 08-01-2015, 09:49 AM   #5
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That is the backflow preventer for the black tank cleanout. Sometimes refered to as the vacuum breaker. It is supposed to prevent black tank syphoning but syphoning is questionable due to the way the piping is routed. there has been alot of issues with your type of preventer, from cracked to being connected wrong. Sounds as though yours might not have tight connections or cross threaded. Also when you disconnect the input from the outside there will be residual water in the tubing that will flow out but it is not from the black tank. From some of the previous posts there is certainly alot of confusion. The cleanout is a self contained system and is not interconnected in any way with the potable water plumbing. The backflow preventer does not provide a vent for the black tank (the black tank is vented already). The preventer is basically a switch that opens when water pressure is applied and closes when the pressure is removed.
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Old 08-01-2015, 09:54 AM   #6
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Mine was leaking as well. Flap was just stuck. Try removing it, cleaning it out and make sure it is operational. I purchased a vacuum breaker at Home Depot figuring I would use it on the washout tank connector but noticed that where I hook the hose to the rinse valve it also has some type on back flow eliminator installed.
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Old 08-01-2015, 09:59 AM   #7
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Thanks. I would have thought the check valve would be located closer to the tank but I guess then it wouldn't be accessible. Luckily I have a new camper and still under warranty. Good time to check on forest rivers warranty service. This is something I'll replace so I just need the part. My water pump was bad from the get go and they shipped me a new one no questions and I had it in a couple days. Let's hope i get the same great service this time. Luckily this has no effect on the rest of my trip. Thanks for the responses.
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Old 08-01-2015, 12:03 PM   #8
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Do you need to use a pressure regulator on the hose attaching it to the black tank flush hookup? Seems 125psi street pressure would be too much vs 45-55 psi with regulator. Why not remove the vacuum breaker as suggested and just put a back flow preventer on the hose too?
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Old 08-02-2015, 07:29 AM   #9
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Removing the breaker and replacing it with PEX (or nothing) is a "bad idea" in my opinion because there would be nothing to prevent black water from contaminating any fresh water source you connect to it.

It also prevents reverse flow of black water from entering the tank spray nozzle that could clog the jets causing it not to work properly.

Additionally, it prevents siphoning of black water out the side of your camper when traveling due to the venture effect on the fill port (should you lose the seal plug).

While I agree the plastic breaker with the rubber flapper can be problematic, there really is no "good" alternative except perhaps a brass one way check valve.

The similarly built plastic "sewer gas" vent breaker used in many homes under the sink serves to allow water to remain in the trap by allowing air to enter via rubber flapper and they can last 20 years with good service; in fact you may have one under your RV's kitchen sink.

Not using your turboflush often (working the flapper) can cause the rubber flapper to become hard and dry where it is in contact with the plastic and can be the cause of your leak. Exercising the flapper works the plasticizers from inside the vulcanized rubber to the surface keeping it pliable (just like using your tires often keeps them from drying out on the surface and cracking/checking).
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Old 08-02-2015, 07:57 AM   #10
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Quote:
Originally Posted by Maxhise View Post
Ok. Just when I thought I knew just about every thing there was to know about an RV, I found something new. My camper is equipped with a black tank flush like a lot of campers. Like most people, I don't use it very often. Usually there is a line at the pump out or I'm just in a hurry and don't bother with it. I do a pretty intense flush when I winterize.

As anyone that has camped for more than 10 minutes knows that there is an unpleasant smell that can come from the black tank when you flush (especially if you have the super fan running and pulling the gases up).

This weekend I'm camping with a sewer hookup for the first time so I took the opportunity to give it a good flush. I ran the toilet until tank was nearly full, drained it and then I turned on the black tank flush. Since I'm camping with water and sewer, I was just going to let it run for hours and I have the drain open

Well, I noticed water dripping from under the camper. After a little research it would appear that the black tank flush hose comes up under the bathroom sink, 90s into a fitting and then goes back down through the floor to the tank. What the hell is this fitting for?

Only thing I can think is that it's some type of vent but I'm not sure. Luckily it only drips when the flush in going and about 95% of the water ran straight back down the water hoses and then dripped into the plastic tray in my basement so there wasn't much mess or damage.

What the hell is this??
Attachment 84716
You were going to let the water run for hours,,, REALY ???
Bet the folks in CA would love to have some of that water !!!
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