I have a 2002 Volvo Penta SX I/O. It came with a motor flush kit, the kind
that has a garden hose fitting on the motor. Is this sufficient for cooling
the motor when it is running on the trailer and out of the water? Or am I
still required to use the "headphone" style hose connection?

I use the boat in fresh water, so I am mostly interested in how I can
properly run the motor for maintenance & tuning purposes.