We spend a lot of time on the road and dry camp quite often. Mostly we get into a campground or find a dump every 4 to 6 days. When camped long term in the desert we have gone as long as 9 days, Pump was starting to complain, toilet was not quite floating and the grey had not yet crept into the shower. indicators seemed right on that day, FW empty and everything else full
After driving up the very steep exit ramp from the wash to the dump area (along with plenty of rocking on the dirt road) the empty Black showed the 2/3 light out everything else lit as usual, the grey seemed to show empty and FW showed full once I filled it. I keep a note of the last time Black was dumped right above the throne.