• rsullivan25
    Hi Everyone.

    I was wondering what is going on with our motorhome holding tanks. Both our black and grey tanks do something strange when draining. When I open the valve, it starts draining as it should, but drains probably 1/4 tank then stops as if it's done It trickles down to a stop, just as if it was empty. I wait for anywhere from 10-30 seconds (because I know it's not done) and it starts to gurgle, then lets go with a flood and finishes emptying.

    Then I move onto the grey tank and same thing - it starts to drain, then "pauses" gurgles and then finishes.

    I'm not sure what's going on? As far as I can tell we only have 1 vent pipe - it's above the bathroom. I was thinking it might be a venting issue, but I'm not sure if it is, or even how to test if that's it? Can I just stick something down there and see if it gets resistance? Or could it be something else?
  • Ray
    To check for a possible venting issue I would think you could try opening the toilet flush valve during the trickle period and it should let air into the tank.
  • rsullivan25
    Thanks Ray I will try that.
  • George
    You might also want to check the vent stack for an obstruction.
  • John J
    That sounds like a good test. If it flows normally, then it is the vent. Likelyhood of being up high where the two tanks tie together, and above.
    Remove vent cap, verify no creature or insects have or could get by. I would use a small "snake" to rooter down the pipe from the roof. Not knowing where the tee is in the vent, I wouldn't push it to far.
    I'm guessing a insects have made a nest. It will be easy to plow through it.
  • rsullivan25
    Turns out it was probably a "mass" in the black tank. I had some septic tank conditioner that I put down the tank. The next time we filled the black tank I drained it without issue. No stopping/gurgling. It just drained normally.

    I think it could have been from a recent cold snap - got down well below freezing for a few days.
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