To add to his post, start up the engine. Let ir idle for few seconds then open the water. It is recommended by seadoo to not run it longer then 5 minutes as the jet pump seals and bearings aren't getting the cooling it needs in the water. You shouldn't rev the engine either. Let it idle on the hose, which the rpm's should be about 3000rpm's. In the water because of the load from the water on the impeller it will idle at about 1500rpm.s Turn off the water, then in a few seconds shut off engine. This prevents water from back flowing in the exhaust into the engine and flooding it.
Karl