Filling and emptying water tanks at camp

Here is what I did. I filled a 5 gallon bucket with water from my hose. it took 50 seconds. Simple math determined the rate was 1 gallon every 10 seconds. Knowing that I can fill my water tank with whatever amount of water I choose with a little easy math and the timer function on my phone.

As for draining the tanks, they're empty when the water stops draining out of them; either that or the drain line is stopped up/plugged. Now if you are relying on the gauges to tell you if they are empty or not, the gauges are rarely reliable. The gauge could read half full when in reality the tanks are empty.