OK, coupla good questions here....
I beech my boat plenty, and I'm a Merc man, but I imagine it's the same regardless. Sometime when you have the boat in the drive, take a look at how little depth difference there is between the lowest and "trimmed" positions... we're talking less than 2 inches! The more you raise the trim, the more the boat wants to turn, due to the orientation of the prop blades turning, as well as the churning around the rear of the hull; thus very difficult to steer, as well as unneccesary stresses on the U-joints. I typically get lined up with my beeching spot, and give it a little go with the trim all down. Once I see it'll stay straight, and I'm not going to abort, I shut the motor off, and run the tilt all up until the bow settles in (keep in mind, our lakes are nothing but mud/silt). At which point I run my bow line to a screw-in stake on the beach. If I'm parking for the night, I will run the trim down until the drive dig's in a bit to hold the boat secure.
As far as flushing, I typically flush as soon as I get home (trailered) from an outing while the motor is still warm. This is done to get out any gunk from the above proceedure, as well as running chlorinted (city) water through my system to help get rid of any Zebra Mollusks that may be around. I flush on the muffs, then drain the system. I don't believe that is the question you are asking though.
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Walt B
"Debt-Charged"Black '07 H210SS6.2L Bravo One turning a 21P HIFive
Wakeboard Tower with Perfect Pass Stargazer version
Missouri River; Kansas City, Mo.