Thanks for all the ideas! I've shared them with Janet (the TM's co-owner) so she has some things to try when she takes it out this weekend.
To add to the info from my original post, we were semi-dry camping with the only hook-up being electric (and that in itself was a rare treat indeed
). We did get some drainage from the gray water tank, but nothing like what would be expected from having used up almost all of the fresh water. Given that, I'm inclined to think that the sensor is actually reporting correctly. Anyway, if there are any updates from this coming weekend, I'll be sure to share
.