Calgon & Dawn treatment for waste tank sensors issues works!

The sensors that come in the tanks are actually electric probes that pock into the tanks. They get coated and then will not conduct the low voltage power that shows the level in the tanks in fractions. RV tank Sensors are electronic
strips that are stuck to the tank and give read-outs in % to a circuit board on the wall.
Just do a Google search. A little expensive but to me well worth it.