you wanna do that BE SURE your engine is running. Otherwise, you will fill
your waterlife muffler until it overflows back into the exhaust manifold and
down one or more of the open exhaust valves, to either hydrolock when you start
the engine or seize the engine with salt water corrosion interally.

When we were running the Volvo that was raw water cooled, there
was an attachment, in the water line inboard of the strainer that
allowed for flushing. About a quarter turn on the fresh water
hose was sufficient for enough cooling. It also worked when you
went to the hard for the winter as it was an easy way to get
antifreeze into the cooling system.

Leanne