Softly is a good way to start. Clean your decks with a good boat soap and a medium boat bush or sponge with a long handle. Rinse everything well and go down below and see where the leaks are. Shut the port that you left open, and go back on deck. Now, get out the sponge (no scratch) and apply some elbow grease to the spots that are still dirty. If you were down below long enough for the decks to dry, wet them. If the water running off as you rinse is whitish, more elbow grease and soap is required. This whitish stuff is oxidized gel coat. Don't use toilet bowl cleaners, carburetor cleaner or penatrol. Go below again and get another sponge (code name; beer). Go on deck and inspect your work. Get the hose going and rinse everything well. If the rinse water looks whiteish, rinse some more. O.K, this is the secret, SCRUB IT AGAIN.