My humble procedure:
I have a pair of 250's. At days end back into slip, tie up and shut down. Hook up both motors to a Y valve splitter we made up. Turn on water and simultaneously begin flushing in down position. Open beer. Start drinking beer while filling wash bucket with another hose. Rinse exterior of motor cowlings and transom area then wash and rinse. Open another beer. Use absorber towel to dry cowlings and transom area. Remove cowlings, check oil, put cowlings back on. Raise motors while still flushing. Wash and rinse exterior lower units thoroughly.... Next (hopefully) unload fish. Open another beer bragging about our fishing prowess (engines still flushing now in up position with catches down and trim pistons retracted). Wash and dry rest of the boat. Now shut off and remove engine flush hoses, slip on cowling covers. Open beer, eye .... the boat, talk more s#!t. Yep, that's 2 over the recommended limit but ... it's the weekend !!