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  1. #1
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    Help Me Understand Black Tank Flush Line Routing

    I noticed the black hose from the black tank flush connection is routed to two blue pex pipes going up to and along the pex hot and cold water pipes to the shower. This had me scratching my head. In repairing a leak from my shower today, upon removing the access panel, I noticed a vacuum breaker which the shower cold water and the black tank flush pex lines connect to. So I am still scratching my head, because while I understand a vacuum breaker prevents back flow, certainly a good thing where a black tank is involved, why would the rest of the plumbing be involved with the black tank? It would seem to me all is required is to directly route the black hose to the black tank. What am I missing?
    Regards, Bruce, Lin An, Kenji & Suki (Our two Akitas)
    2019 Solitude 310GK-R
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  2. #2
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    I think you’ve tracked the wrong line. Only the black tank plumbing should be on the vacuum breaker. Two lines, one to the tank and one to the flush port.
    John & Kathy
    2014 F250 Lariat FX4 6.2L SBCC
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  3. #3
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    You may be right, but I closed up the access panel so I cannot double check. I do recall the two lines connected to the vacuum breaker, could have sworn on a stack of bibles the the cold line was also connected to the vacuum breaker, could be wrong. But assuming you are correct, I am having a hard time understanding the need for a vacuum breaker for the black tank rinse if indeed no other lines are involved?
    Regards, Bruce, Lin An, Kenji & Suki (Our two Akitas)
    2019 Solitude 310GK-R
    2015 Ram 3500 Big Horn CC, TD, Aisin Tranny, DRW

  4. #4
    Site Sponsor sande005's Avatar
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    Plumbing codes. The vacuum breaker serves as a backflow preventer. In case any "stuff" from the tank gets sucked backwards into the hose, and then into the campground fresh water plumbing - polluting everyone's water used for drinking/bathing/etc. Very rare, but there have been bad disease outbreaks due to similar happening in commercial/municipal water systems in the distant past. This ensures the dirty does not ever mix with the clean, even if there is a major fault in the main water system that results in reverse flow.
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  5. #5
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    Got it thanks, that splains it.

  6. #6
    Site Sponsor SolarPoweredRV's Avatar
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    Quote Originally Posted by BB&LAB View Post
    You may be right, but I closed up the access panel so I cannot double check. I do recall the two lines connected to the vacuum breaker, could have sworn on a stack of bibles the the cold line was also connected to the vacuum breaker, could be wrong. But assuming you are correct, I am having a hard time understanding the need for a vacuum breaker for the black tank rinse if indeed no other lines are involved?
    The vacuum breaker is required so that black tank water can't be siphoned back into the city water supply if the city water pressure were to somehow disappear suddenly (broken line somewhere) and you weren't there to shut off the spigot. The black water could easily be siphoned into the city water supply and contaminate it.

    By-the-way, they place the vacuum breaker up with the shower lines because that is the only place they can get the required elevation to prevent siphoning.
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  7. #7
    Site Sponsor Richter's Avatar
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    We had a leak where one of the lines connects to the shower control/faucet. I pulled the faucet and found that the “pex” wasn’t. It was flex tubing, blue and red, like the pex, but it had a braided appearance, not the solid color of pex. This is a known issue and has been the source of many leaks for other users, as the inside diameters are not the same for this piping and regular pex. They use fittings designed to fit the pex piping, but they are not the right size for the flex. A little “tighten it as tight as you can with a pex clamp and hope that it don’t leak” sometimes works and sometimes doesn’t. There have been many threads about this on this forum.

    I also noted that the vacuum breaker was in the same area, and they were all cable-tied together, so that they appeared to be physically connected. There were a couple of additional ties, further down behind the shower wall, that I couldn’t get to. I ended up leaving the old section of red pipe as a part of the bundle, not connected at either end, and I ran a new piece of pex up, then hooked the ends to the fittings that had been connected to the flex piping.

    Eventually, I may replace all of the flex tubing, as every coupling is a joint that is just waiting to find a good reason to leak in the middle of the night.

    Thank goodness for water detection alarms at 0400. It could have become a real mess.
    Tom and Janice (known as Tom in PGH on the “other” forum)

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  8. #8
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    Quote Originally Posted by Richter View Post
    We had a leak where one of the lines connects to the shower control/faucet. I pulled the faucet and found that the “pex” wasn’t. It was flex tubing, blue and red, like the pex, but it had a braided appearance, not the solid color of pex. This is a known issue and has been the source of many leaks for other users, as the inside diameters are not the same for this piping and regular pex. They use fittings designed to fit the pex piping, but they are not the right size for the flex. A little “tighten it as tight as you can with a pex clamp and hope that it don’t leak” sometimes works and sometimes doesn’t. There have been many threads about this on this forum.

    I also noted that the vacuum breaker was in the same area, and they were all cable-tied together, so that they appeared to be physically connected. There were a couple of additional ties, further down behind the shower wall, that I couldn’t get to. I ended up leaving the old section of red pipe as a part of the bundle, not connected at either end, and I ran a new piece of pex up, then hooked the ends to the fittings that had been connected to the flex piping.

    Eventually, I may replace all of the flex tubing, as every coupling is a joint that is just waiting to find a good reason to leak in the middle of the night.

    Thank goodness for water detection alarms at 0400. It could have become a real mess.
    Put some thought in before replacing the flex. Pex transmits noise and vibration more than the flex, and in certain situations with limited access it can be nearly impossible to get Pex aligned so you can get a threaded fitting started. There are proper fittings available to couple Pex and flex or you can make them out of two threaded adapters
    John & Kathy
    2014 F250 Lariat FX4 6.2L SBCC
    2014 Reflection 303RLS
    SW Indiana

  9. #9
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    Quote Originally Posted by jkwilson View Post
    Put some thought in before replacing the flex. Pex transmits noise and vibration more than the flex, and in certain situations with limited access it can be nearly impossible to get Pex aligned so you can get a threaded fitting started. There are proper fittings available to couple Pex and flex or you can make them out of two threaded adapters
    There is some merit to this, for example the water pump inlet and outlets. Our Solitude 310GK had pex pipe on the outlet side, when I replaced the original pump with a Shurflow pump and Shurflow recommended flexible hose on both sides to minimize noise. Another pro to flexible hose is it does not require elbows which tends to reduce water pressure to make a bend. Having said that the flex tubing installed is not the best of quality and can be a weak point. In cases where flex tubing might be a better option, perhaps replacing with braided hose is a better choice.
    Regards, Bruce, Lin An, Kenji & Suki (Our two Akitas)
    2019 Solitude 310GK-R
    2015 Ram 3500 Big Horn CC, TD, Aisin Tranny, DRW

  10. #10
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    Quote Originally Posted by SolarPoweredRV View Post
    The vacuum breaker is required so that black tank water can't be siphoned back into the city water supply if the city water pressure were to somehow disappear suddenly (broken line somewhere) and you weren't there to shut off the spigot. The black water could easily be siphoned into the city water supply and contaminate it.

    By-the-way, they place the vacuum breaker up with the shower lines because that is the only place they can get the required elevation to prevent siphoning.
    Is it normal for water to run out of the black tank flush connection when disconnecting the hose? Maybe because the connection is lower than the black tank input?
    Steve & Ann Ellis
    2018 Reflection 303RLS
    2019 Ram 3500 6.7 Cummins

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