Re: flushing 1970 25 johnson seahorse
agreed. These motors weren't designed to run on muffs, so it really is best to put it in a tank with water filled to a couple inches below the main exhaust port. Otherwise, you'll have to devise a contraption of some sort and/or or modify a pair of existing muffs. I've seen people make adapters that involve a small piece of wood (or aluminum) cut to the same size as the water uptake panel found just above the cavitation plate to which a garden hose adapter mounted in it. They then screw on the wood/aluminum plate they made with the hose attached and turned on to med-high pressure, but it's probably cheaper and easier to just find a big old trash can.
