I'm with Jason--
Ever consider a self serve car wash? $2.50 for four minutes and they provide the soup and brush. You wouldn't even have to take the yaks down off the rack.
I have a big container with a lid on a hinge-- I fill it up with water and car wash soap before I leave the beach. Put my seat, straps, PFD, ect in it and drive home. By the time I get home my gear is nice and clean from the sloshing it went through on the way home.