Black holding tank won't drain past 2/3

Ritkei wrote:
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?

Sounds to me like you have a bad sensor. I just replaced mine and noticed on one of the sensors I pulled from the black tank that it was all crusty. Most oem sensor are nothing more than a little button type stud that sits against the wall of your tanks. Any fluid running down the sidewall will come in contact with the sensor and send out a reading.

get yourself one of these its the only sure fire way to know when nothing more is coming out of your tanks. Plus, if you have a black tank rinse you will be able to know when its "clean" when you start to see clear water running out.