Flush the engine with fresh water. Some outboards have an attachment for a garden hose to make the job easier. Otherwise, use "earmuffs" to reverse flush outboards and sterndrives. Idle the engine when flushing, making sure it doesn't overheat, until the water flushes clean. Clean all outboard telltales with a piece of wire, and store the engine in a vertical position to make sure the water drains completely. Even a small amount of water left in the engine can freeze and cause big damage. Inboards and sterndrives require refilling with propylene glycol antifreeze to prevent small ice pockets from forming, which can crack the block. [links]