I'm wrapping up the installation of my SCAD Solo holding tank monitoring system. It's time to calibrate it. The instructions have a simple procedure to set the firmware's High and Low calibrations. One is done with the tank empty (easy). One is done with the tank full (not so easy). I had planned to flush 18 gallons of water down the toilet to be sure it was full and calibrate since there is no other way to know when it's full. The folks at SCAD say the calibration will be off since water doesn't have the "salinity" (his word) of waste. I still don't understand how the system works, but I'd like to figure out how to get closer to the "dialectic constant" of the fluid I am putting into the tank. It's a Catch 22. I bought the monitor to be able to know when it's full, but I can't know it's full until it is. Any thoughts on how I might top my aluminum tank off accurately with something close to the real thing? FYI, we only use it for number 1 unless it's a real emergency. For more than you ever wanted to know, here is some information on the types of technologies used to measure. SCAD uses the Capacitance design.