Forum Discussion

andybren's avatar
andybren
Explorer
Sep 24, 2020

black tank flush port

I have a 2008 coachman Pathfinder diesel pusher which has a hose connection in the wet bay for a black tank flush. My question is ; do my other valves in the wet bay need to be in a particular configuration for the water to actually get into the black tank and do its job? No information is posted in the bay other than the one that says to open black tank drain before turning on the water.
  • wa8yxm wrote:
    As the first reply said the tank flush line is 100% independent of all other plumbing. And in fact I suggest even using a different hose to feed it. and when not pushing water into the tank DISCONNECT it.

    There are safety devices to prevent backflow from Tank to the water system. Mine has both a spring check valve at the tank and a vacuum breaker above the tank... BUT even with Belt and suspenders you can lose your trousers. (Thus I "Air gap" the line to insure no possible backflow.


    I literally have a brown colored hose for the black tank flush. That's all it's used for.
  • I forgot mine once and had water coming out of the roof vent. 2 hours later after washing the coach and surrounding area, I vowed never to forget to open the valve while flushing...Dennis
  • wa8yxm's avatar
    wa8yxm
    Explorer III
    As the first reply said the tank flush line is 100% independent of all other plumbing. And in fact I suggest even using a different hose to feed it. and when not pushing water into the tank DISCONNECT it.

    There are safety devices to prevent backflow from Tank to the water system. Mine has both a spring check valve at the tank and a vacuum breaker above the tank... BUT even with Belt and suspenders you can lose your trousers. (Thus I "Air gap" the line to insure no possible backflow.
  • If you haven't used it you should fist locate the Anti-Siphon Backflow Preventer device
    It is installed at least 2' above black tank...typically inside bathroom sink cabinet
    It acts like a check valve when water supply is turned off...allows air to enter tank side line so water drains back into tank
    When water supply is ON the disc is pushed up blocking the air inlets
    If it doesn't seal off...water POURS out and can flood bathroom etc

    Water supply goes in bottom connection and flows to tank nozzle out the side connection

    Someone should watch it when first using to make sure it doesn't leak



    Cheap plastic ones are typical...better brass ones are available


  • You can close the valve while flushing, you will put approx 5 gallons a minute into the tank. Open & refill as needed until the tank waters running clear. DO NOT GET DISTRACTED, that can lead to serious damage. Keep the black closed except dumping or flushing.
  • The black tank sprayer is totally independent of anything else in the bay. From the female hose connector, there should be a back flow preventer valve and then pipe to the sprayer. It is wise to open the black valve just in case you forget you are flushing the tank to keep it from overflowing