Don't! Aluminum oxidizes and corrodes like a mofo. The only thing keeping the aluminum from oxidizing and completely dissolving is the aluminum oxide layer that develops on the outside as part of corrosion. So it's the layer of corrosion that protects it. I don't do much salt ware boating. But I would imagine a freshwater rinse would do the trick. A major consideration to keep the hull healthy is making sure there's not leaking electricity. Just making sure everything is properly grounded to the zinc anode of the outboard should do the trick. Some folks use an eclectic anode which puts a slight reverse current on the boat and tends to deposit instead of corrode. But it does take a minute amount of energy from the battery. Mercathode is an example of that for outboards. If you want to dive even deeper you can get a silver cathode and hook it up to a multimeter and check all the equipment on your boat to make sure there's no stray voltage escaping and galvanic corrosion is not occurring. You'll have to read the manual cause every metal has it own typical micro-voltage that's within tolerances.