We have a 2021 3761FL and it has 2 44 gal black tanks with the associated flush and dump valves. The level sensors have NEVER worked reliably from new! Dawn, 5 gallons of water and a long drive helps some, but they soon read 2/3 all the time again. Just dump your tanks weekly and you will be fine.
2021 Montana 3761FL, 6-100ah LIFPO4 batteries & 1700 watts of solar panels w/ Multiplus II 3K inverter and 30amp DC to DC charger from truck.
2019 6.7 diesel F350 DRW with Banks derringer and 4"exhaust, airlift bags, 25k B & W Companion hitch, 45 gal. aux. diesel tank and 14k Winch, just in case!