Re: Run the motor on the hose
Yes, the rubber impeller in the ob water pump must have water at all times, or it will suffer premature death. Some motors (many Tohatsu, Nissan, Mercury) can run on a Flushing Adapter -- screws into the motor, and attaches to a hose. Many others can use ear muffs, but some cannot accept the Ear Muff adapters, due to the configuration of the water intake.
Small (under 15 hp) motors can usually idle in a large trash can. You can't "pour the coal to it" though, because the water splashes out of the barrel, but it will prove out the systems as "working"
Still, you can't get a "real world" cooling system test unless you launch the boat and run in the water.