When I do mine, I get a supermarket shopping/carrier bag to cover the alternator, then using the PW to quickly wet the bay. Then spray with a Megs bottle with foaming head filled with a degreaser like R222 Total Auto Wash and agitate areas with various brushes, then wash off being carefull to to 'flood' the engine bay. Dry using MF towels. Leave and continue to clean/detail the rest of the car, buy which time the bay should be nice and dry if it is a warm day. Then using your engine dressing product of choice - 303 Aerospace dress rubbers, plastics etc, then leave.