What size water pump & bladder tank for washdown?

What kind of specs should I look for in a good washdown system to put on my
boat?

We have a houseboat, and primary concern is just washing down the top,
front, & rear decks - bugs, muddy footprints, spilles drinks & food, etc.

I see pumps rated from 2.0 GPM on up, pressures from 20 PSI up, and
accumulator tanks from 16 oz to several gallons.

Just not sure what these specs will do in a real world situation.

Thanks in advance...

cag