Leave the engine running, spray down with degreaser, use a brush if you want to scrub, spray off with hose. Take towel and wipe dry big parts. I did this everyday when I worked in the reconditioning dept of the dealer I work for with no issues. Most of the time I didn't even leave engine running, but I have seen others get water in the plug cylinders and cause a misfire. This is an easy fix though as the water can simply be blown out. Only takes about 5 minutes too and cleans it very thoroughly.