Can I just simply flush with the muffs on
for like 5-10 minutes with the engine running?\


Same engine and outdrive I have on my Starcraft. If your's is set up
for salt water, with fresh water cooling, then the muff's won't flush
the fresh water side. You may basically have a "heat exchanger",
where engine heat is transfered to a fresh water system, through the
exchanger, and then to salt water from the lower unit pump.

Does your manual describe this?
Do you have a heat exchanger on the engine?

If so, you will need to flush the fresh water side seperately.

If he's just trying to flush out the sal****er after each use, why would he
have to flush out the closed freshwater circuit. Aren't the freshwater and
raw water systems isolated?