I bought a spare ShurFlo pump. It is rated as taking 7.5 amps but says to fuse its line at 10 amps.
I frequently use 5 gallon containers to refill my fresh water tank. I wired the pump with a connector that fits a 12v source I have, 16g wire, a 10 amp inline fuse, an inline switch, and garden hose fittings. I put one hose on and put it in my water container, and the other hose into my fresh water tank fill. Works great. I just wanted to be sure the switch was OK.
I will buy a different switch. Of course, it will run for no more than about 4 minutes at a time until I have to go back to the hydrant to refill them.