I made one
I amde one from a tackle box, a 12 volt wash down pump from boat us, some hoses and fittings, and a $40 recharable jump battery from boat us.. One end of the hose went over the side and then to the pump intake.. the output side of the pump had the wash down hose.. and the jump start battery provided power.. took about three minutes to assemble.. the battery lasted nearly all season before recharging it.. and the pressure was the same as a regular wash down.. the difference was that I didn't drill any holes in the boat.. kept the whole think on board.. and only brought the battery in once to chage..