Forum Discussion

Ritkei's avatar
Ritkei
Explorer
May 30, 2013

Black holding tank won't drain past 2/3

After 4 days of camping we have a full holding tank. I open the black valve and hear a rush of fluids for about 1 min, then nothing. Check the tank level inside and it shows 2/3 full. After searching I found a post that suggested filling all grey tanks and pull all the valves at same time, causing enough of a vacuum to get the holding tank to drain. This worked once and now I'm stuck at 2/3 full again. Never seems to drain below 2/3 full. Any ideas or tips tricks?
Seeking Advice
  • Bonefish's avatar
    Bonefish
    Explorer
    May 30, 2013
    Depending upon how the commode is plumbed. Many allow you to open the dump valve and see down into the holding tank (flash light required)and check the fluid level. Tank gauges are notoriously for being wrong.
  • tmmar's avatar
    tmmar
    Explorer
    May 30, 2013
    Are you sure that is not empty? You can get false readings from the tank level gauge if there is something caught on the sensor in the tank. Try filling with clean water and draining again to see if that will dislodge anything on the internal tank sensor. Also, do you have a black tank flush? If so, you should try flushing the tank with that.
  • Roadrash450's avatar
    Roadrash450
    Explorer
    May 30, 2013
    You may have a bad sensor in the tank or TP/poop stuck to it giving you a false indication. Very common for this to happen

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