My RV is 29 years old. We are its second owner. We have had it for about 10 years now.
Our sensors work fine.
Now, they are not instantaneous in response. If you drain the tank and immediately check the levels, the sensors will say the tank is still full. This is probably because the side walls of the tank are still very wet and electrically conductive and so the higher-level sensors are still wet and think they are submerged still. But, if the tank has been allowed to sit for a bit, then the sensors work fine.
You'll note that I never do anything special to my tanks. All I do is put one of the "poop pellets" down the toilet every time we use the RV. And, at the end of every trip I put a block of wood behind the flush lever to keep it flushing until the black tank is completely full before dumping. But I never go to any of the lengths that others try to go to to keep their tanks clean. I have never sprayed it out. My dad, in an attempt to be helpful, dumped ice cubes down the toilet the day we bought it, but I doubt this did much.