That's what I have been thinking. So I understand what your doing with the hose and fresh water rinse. Doesn't the water pump still bring in the Saltwater... So in really your deluting the saltwater with fresh?
LG
Try this with the boat in the water....flush with fresh water hose a idle for about 3-4 minutes. Then open the rear manifold plug (either port or stbd) and taste the water....it's fresh.