The sensors in the tanks are notorious for incorrect readings. I also have a black tank flush and no matter how long/often I use it my black water tank shows 1/2 or 3/4 full. So what I do is look down the toilet as I flush and if I can see the waste water level I then dump the black tank.
Joe, Joyce , 4 Kids and 3 Dogs.
2004 V-10 Excursion with Hellwig sway bar, Roadmaster Active Suspension, Bilstein shocks and steering stabilizer, Super Duty Tow Mirrors,
3.73 Gears, Reese dual cam, Prodigy brake controller.
2010 Jayco Jay Flight G-2 32 BHDS