Here is a trick I learned when I had a Class B. Don't use a shower head or handheld shower head. Use a kitchen sprayer hose and head which will cost you from ten bucks on up. They put out good pressure and when you finger is off the hold down lever that baby is OFF and you don't drip or waste a drop of water. Also, you will find the pressure seems to be higher than a shower head. Like some one else suggested, fill a gallon jug like a milk carton with water and see how long it takes.
We (two of us) get six good showers, shower daily and our 38 gallon tank plus 6 in the hot water tank lasts 3 days, 4 if we take 8 really quick light showers. We wash our dishes over that time period and NEVER use campground showers or toilets. We very seldom stay where there are hookups. You can wash and rinse your hands well with less than a pint of water easily.
