Using an outboard’s built-in flush fitting works well on boats kept in the water. Again, check your manual for specifics to your engine. Generally speaking, immediately after you shut down the engine at the dock (this ensures that the engine is still warm) and with the outboard tilted up, connect a freshwater garden hose to the flush fitting, turn the spigot on full blast and let it run for about 15 minutes. Do not turn the engine on during this process because water only trickles down to the water pump. You can damage the pump’s impeller while running the engine with this flush method.