flushing outboard correctly

[TUBESEARCHER]

my 2010 T60 Yamaha has the waterhose attachment for flushing critical engine parts.
BUT is that waterhose attachment just for flushing while the engine is off?

do i use engine ear-muffs waterhose connectors, on the lower-end water intake area while flushing while the motor is running?

I'm confused by this bc i dont want to harm the $7k engine

[rodbolt17]

at a dead idle only, the hose fitting works very well.
anyting above i use both.