i know down wollongong they have taps at most ramps to run your motor and i think a quick rinse, but i havent noticed them up here, not that i have realy looked.
i usually wash my boat and trailer at the local car wash after every seshion cost me $5 first i have $2 rinse then $1 wash which runs out but the foam still spreads to the remainder then $2 rinse! and i run my motor at home probably not allowed though!