[DutchmenSport]

All you have to do is dump your black tank and flush it out as best you can. Then add 5-10 gallons of water and some Dawn Dishwashing Liquid and take the camper on the road. The more turns, the more bumps, the more stops and go's you experience will cause the tank water to slosh back and forth and side to to. This sloshing will pulverize the sensors, cleaning off anything stuck on them, causing false readings. When you reach your next destination site, or return home, dump the soap water if you can. The sensors will probably be reading correct again (for a while). So, you need to do this every time you move the trailer.

Backflushing from the grey tank, using the black tank flusher, and using a toilet wand on the end of a garden hose will also help clean the tank out, thus making the Dishwashing solution even more effective.

It works and I've been doing the Dawn water slosh around method for over 20 years, and 4 RV, my black tank sensors have always worked.

I don't depend on them though. I've learned how long I need to go before dumping. Once you live in your camper long enough, you'll get a good feel for it too.