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Water leaking when dumping gray water

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  • Water leaking when dumping gray water


    We just returned from the First trip out with our brand new 200MK. I failed to notice that the gray water and black water valves were both open from the dealership.

    Both tanks were 2/3 rd full when we dumped at the dump station. When I dumped the gray water, I noticed that there was water leaking around the gray water pipe as it exits through the bottom cover of the TT. I assumed that there was a leak in the gray water pipe. However I have since tried to reproduce the problem by filling the gray water tank to 2/3rds full and then emptying it - both times there was no leaking around the gray water pipe.

    I now think that having these two valves open when jacking up the TT at the campsite may have caused black water to flow into the gray water tank - perhaps causing the gray water to leak out of the tank vent. Except that I don't know anything about the gray tank vent to know if this hypothesis makes sense.

    Does anyone know if this explanation for the leak is feasible - or if there is another possible explanation?


  • #2
    Your theory doesn't work since the tank vents are on the roof.

    My guess is you have a small leak on one of the fittings on your grey tank plumbing between the valve and the outlet where you hook the stinky pipe. You didn't see anything leaking on subsequent fill/drain attempts because the tank was free to drain as soon as you open the valve not allowing pressure to build up in the drain piping.

    When you noticed the leak, the valves were open and the head pressure from both the black and grey tanks were in the drain pipe because you had the outlet capped. I don't know what size your tanks are but just guessing they are 45 gallons each and they were both 2/3 full. That would equate to approximately 60 gallons of water (60 gal X 8lb 6oz = 502.5lbs of head pressure) Unfortunately, the only way to know for sure would be to drop the underbelly and inspect.
    Jeff and Debbie
    2021 Imagine 2250RK
    2015 Ram 2500 6.7 CTD Crew Cab Short Bed Factory Air-Ride Auto Level
    USMC Veteran


    • #3
      I might guess that you have a seal issue in the top of the tank where the inlet is. Having both tanks open and moving the unit allowed water to 'slosh" between the tanks possibly causing one to become completely full. If you are trying to repeat the issue without moving the unit, the "sloshing" is not present which identified the issue.

      Also If you are filling the tanks any way other than how used when camping you will not know if the issues is not say in the shower drain. You might try filling the grey tank part way with the shower and part way with the sink(s) to see if the issue is actually one of the drain lines.
      Tow Vehicle: 2018 GMC K2500 Denali Diesel
      Coach: 303RLS Delivered March 5, 2021


      • #4
        Thanks for the quick responses!

        I didn't see any leaking until we were at the dump station - I am almost certain we would have noticed any leaks from normal usage - we did use the shower, and sinks throughout the trip.

        I actually didn't notice the leak until I emptied the grey water tank. I had already emptied the black - but I don't actually know if it was leaking before I opened the grey water tank. I was kinda busy trying to contain the black water already in the pipes - luckily in the 200MK the valves are almost at the end near the fitting so there wasn't much spillage tp clean up.

        For my experiments with the grey water tank I filled it from the kitchen sink to 2/3rds full and then drained it - no leaking occurred. Then I filled it again and drove it for 20 minutes - far longer than the drive from the campsite to the dump station and after this still didn't notice any leaks. So I don't think it is sloshing of the water - I think it the combined pressure and volume of the black and grey water.

        The black water tank is in front of the grey water tank in the 200 MK and the grey water tank is behind the rear axle. so lifting the front of the TT with 2/3rds full black water tank would have pushed black water into the grey water tank. but I don't really want to try the same exact situation again as an experiment so I will probably drop the rear underbelly cover and take a look to see if I can see a problem.

        thanks again!


        • #5
          aorrville -- lots more info here on the forum to discover. I hope you'll take a moment and check out the Welcome Letter to New Members at

          Forum moderators are not GD employees--we are volunteers and owners presumably just like yourself. Unless specifically mentioned otherwise, we have nothing to gain should you choose to purchase a product or engage a service we discuss on this forum.

          Howard, 2017 Ford F-350 DRW, '19 315RLTSPlus


          • #6
            Like I mentioned, it could be that when the black tank pushed into the grey tank it pushed the water up to the intake connection. Likewise depending on how you drained the HWH it could have leaked behind the wall during the drain process if you used the drain by the burner. You may try the city water connection drain method you used before and see if you get the same "leak".
            Tow Vehicle: 2018 GMC K2500 Denali Diesel
            Coach: 303RLS Delivered March 5, 2021