Don't waste your time & energy, of the last 3 rvs I've had none of the sensors were worth the trouble. Our toilet has a certain sound when flushing to let us know it's time to dump or I just dump once a week, the bath grey I leave open til a day or two before dumping black & the galley grey will hold til then. Others will have magic potions to clean sensors, but in my experience it works now but not later so I just quit fretting over them, don't ever look at the levels anymore.
Danny & Linda
Sold our '13 Thor Redwood 36 FB
Currently RV & truckless