Re: Screw on flushing kit?
it's imoprtant to determine whether you can run the motor on a hose flush kit or not. Generally, if water isn't coming up from the bottom through the water pump, you fry the water pump if you run it.
So for the built-in hose on a 2003 Yamaha, you don't run the motor, you just hook it up and let it the water pressure do its thing. (so what do you do about the thermostats not opening?)
Lots of people don't know this and lots run the motor. My guess is that this is usually when they just pulled the boat out of the water, so it's still wet enough to survive. Or they just got lucky.
It's possible that some built-in flushing systems overcome this; I'm just saying, don't assume.