Also after a washdown pump and wondering,  don't want something that trickles out.

I found that the smaller volume pumps are at best wimpy. Self priming a must.
But I overcame the problem by putting the water through my tuna pump and then the wash down. Gives me excellent blast pressure.
The wash down hoses breakdown quickly in the uv, I'm currently using a cloth covered expandable hose which is currently only half a season, so ok.

Im like Walu...
Have a intake on the bottom of the stern, with a $25 bidge pump mounted on a home made alloy bracket.. going to a hose .. this Tess off to the home made  50Llive bait tank and to garden coupling, that attach a short garde hose and garden fitting like Walu above.
Ok it is not a blaster pressure.. but spray / wet bait board sides etc down, a brush from a $1 brush and shovel set, to lift anything that even a high pressure short of water blaster will not lift... then rinse off... without filling the boat with water. Then simply rinse of the salt with fresh water when get home.
 Get upto around 10 knots and dont need to turn on the pump as the pick up gets enough pressure.

PS replaced the collapsible hose in the pick with measures garden hose and the gun with Walu pic above.. note the 3 outlets in the livebait tank.. 1/2 full and drain in the bottom


Yes I can see the use of a high pressue / volume washdown on a larger boat.. but trailerboat.. no