Because I found in the rv manual that simply plain water with minerals in it will foul the sensors, I HAVE purchased the sensor cleaner that is available that actually does remove the minerals. CG well water is the big culprit for that.
I clean regularly with a lemon cleaner but I have found that using that 'sensor cleaner' does remove the deposits that prevent them from woring properly.
Unlike many, my sensors have always worked in all the different RV's I have had. I do believe that it because I clean the tanks 'often' and add a bottle of sensor cleaner every so often.