We are primarily dry camping this year, so I'm getting to "know" my fresh and gray tanks better than last year.
So far I've been able to confirm on multiple trips that my gray sensors will show 2/3 full before my fresh sensor shows I'm 1/3 empty.
I haven't measured for specifics, just confirmed they aren't very accurate.
On the good news side, we managed 4 Navy Showers last weekend without any issues. Our tanks are 37+6 Gallons Fresh, 37 Gallons Gray.
PS - I noticed the sensor is labeled "Grey" not "Gray." Were they aiming for some upscale British image of the waste water?