My OEM tank sensors are usually fairly accurate on both grey tanks, but the black tank frequently is misleading. I have sometimes just drained the black tank, KNOW it is empty, but the sensors will read full. Other times, same scenario, and they will read empty.
Before next camping season, I have decided to install HORST Miracle Probe sets in all 3 tanks. Have heard nothing but praises for them, and they are guaranteed by the manufacturer to remain accurate. There is a shield over the black tank sensors to keep toilet paper from "shorting" the sensor, so it won't affect readings. They are supposed to fit in the original holes, and use original wiring.
These Horst probes are available on Tweetys, ebay, Amazon, and other places, but NOT from Camping World (My local Camping World never heard of them).
2003 Ford F-350 V-10 Crew Cab 4WD Long Bed
2004 Jayco Designer Medallion 29 RLTS 5th wheel
Bill, Gayle, and Mindi (dachshund)
Retired at last !
Nothing is foolproof to a sufficiently talented fool.