Mr. Luddite wrote:

I got curious regarding the discussion of rinsing an outboard using
the garden hose flush port versus muffs on the water inlet so I did
some reading. I had a Yamaha 250 four stroke on one of my outboard
boats and seemed to remember reading something about it.

First of all, it is not recommended that the engine be run while
flushing using the flush port. Yamaha states that *if* your water
supply pressure is sufficient to generate a steady stream from the pee
hole, it's ok to run the engine while flushing at idle RPM and for no
longer than 15 minutes. If the flow is *not* sufficient to generate
a steady pee stream, Yamaha says to use muffs in addition to the
flush port if you want to run the engine.

The flush port injects water after the thermostat which will be closed
if the engine is not running. If somehow water can still get down to
the inlet passages and impeller, the impeller won't be turning (unless
the engine is running, in which case it would simply pump the water
back in the opposite direction), so I don't see how it can be rinsed
off. The impeller would tend to seal off any water from running
through it with the engine not running.

So, I still question if using the flush port thing really does
anything to rinse the water inlet and impeller, extending it's life.

Here's some collaborating information:

http://www.saltawayproducts.com/FlushPortPage.htm
I don't trust the port and always use the muffs and run the engine.