All of the tank sensors are very innacurate after normal use. I have used all kinds of additives, cleaners, sensor cleaners and snake oil and NOTHING WORKS!!! I have done the Geo method, added ice to the black water tank when moving, added soaps and a small amount of water when moving, and NOTHING WORKS!! At least not permanently.
The easiest way for me, as a full timer, is to use the "burp" method on the black tank. I generally leave the grey tank valves open until a few days before I will need to dump the black tank- experience tells me that it will be about a week- just to rinse the sewer hose.
I added a Valterra valve between the trailer and sewer hose to prevent the little "surprises" when you take the cap off the sewer line. Then buy yourself a clear fitting to go between the trailer and sewer hose to see what is being dumped, then keep a close watch as I dump the tank, then use the built-in tank flusher and then finally, use the soapy water in the grey tanks to final rinse the hose.
Use a toilet paper that is septic safe and use plenty of water when flushing the toilet.
Bottom line is that I ignore the gauges and have been doing so for years. Its an exercise in futility to try to clean the sensors and keep them clean.
2011 Heartland Landmark Grand Canyon