Key to keeping sensors working... don't let toilet paper and other sludge dry on them. The other is making sure none of the flimsy wires have come loose from the contacts on the outside walls of the tanks.
Yes, it's a simple, cheap system. But I'm convinced 95% of the problems stem from not properly THOROUGHLY flushing tanks from day one when the coach was new. Why do some have troubles and others don't? Either loose screws on those contacts, or not flushing properly.
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