On Fri, 4 Jan 2008 01:42:15 -0800 (PST), Matty F
wrote:

I would guess that it makes no difference to the flushing quality, and
I reckon it's unnecessary and dangerous to have the motor in gear with
the prop turning while flushing.

It also has to do with getting water to the engine. With the prop in
gear, in a confined space, there is decreased water flow to the
engine.

There is no need to turn the prop anyway.