Mine regularly reads empty when I first empty it. After an hour or so, even before it has been used again, it will read 1/3 or 2/3 and within 24 hours it will read full when I know it is empty. I just wait until I get an air bubble during a flush and then empty it. I know this will be about 2 1/2 weeks for me.
2006 GMC 2500HD CCSB 4x4 Duramax/Allison, Titan 52 gallon fuel tank, Prodigy Controller, B&W Companion Hitch
2010 Jayco Designer 35RLTS, Cummins/Onan RV QG 5500 EVAP, Progressive Industries EMS-PT50C, TST Systems 507 TPMS, RV Flex Armor Roof