I learned something just a week ago about cleaning the holding tank sensors and it worked just great. The trick is to start out with empty tanks. Then get a bucket and put in a cup or so of Cascade auto dish detergent, then add about 5 gallons of REALLY HOT water to the bucket and mix. Pour down the drain. Repeat if the black tank sensor is also not reading properly and dump down the toilet. Now drive around for a while (1/2hour or so) so the mix sloshes around . I made lots of corners. Let it sit for another 1/2 hour then dump. Another way would be to add the mixture to your tanks before your next trip, then dump when you get to your destination. The Cascade cuts thru grease and sludge, and the hot water washes the crud away. When I dumped after the cleansing I was amazed how much crud came out(I have a clear 90degree elbow on my dump so I could see it). All the sensors are now working properly.. I will do this before most trips in the future! Hope it works for you..