The sensors are unreliable. There are some aftermarket sensors that folks have tried with some success.
I've learned how long we can go without dumping based on the number of people we have with us on a trip or if it's just my wife and I. There have been a couple of times where my guess has been wrong. I carry a blue boy tank for just that reason so I can dump off some and give us another day or so before having to dump.
Be sure to train guests on how to use the sinks, shower and toilet so you can extend the length of time before needing to dump. Too much running water will fill the tanks quickly.