When we are getting ready to go from one place to another, I typically drain black and grey tanks, add a little water and dish washer soap, laundry detergent, Dawn, Lysol, or whatever is handy and let the slosh clean the sensors. 95% of the time, sensors work great when we arrive at the new spot. After we park again, they will get dirty and quit working again - sometimes in a short time, sometimes longer. We have learned enough through the years that we do not need sensors to tell us when tanks are full. Cleaning them and seeing how long before they get dirty again is kind of a game we play (easily entertained).