Tote along tanks
I use one of the two wheel models that has a bar to attach to the ball on your hitch. Mine is a 15 gallon. I would not want to move one that was much more than 20 or so gallons. Keep in mind that water weighs about 8.6# per gallon so a 15 gallon tank will weigh around 125#.
There are two brands and they both seem to work just fine.