[travelin texans]

Best advice is don't drive yourself nuts trying make the sensors any more accurate than they currently are, it would be a waste of time, effort & money, as stated just learn your tank.
As far as odors, look on line for the Geo method, it's cheap & effective!
Most of the additives for rv tanks are just deodorizers, actually don't help much with solids.
The enzyme additives such as RidX or others only work if left in the tank for weeks/months plus if anti bacterial soaps &/or bleach are used they neutralize its effects anyway. Rinse black tank thoroughly, may take several rinses, then add the ingredients of the Geo Method.