I have used Simple Green with a garden sprayer. Easy to do, just pour some in straight our of the bottle and soak the old oily stuff down. It works even with engine cold. Come back a half hour later and hose it all down with a garden hose. You can avoid getting car wash spray on a hot engine this way. I have read here warnings about getting any cold water on the IP, it is a very precision part that does not like to get a cold shock.
Cost of a gallon of Simple Green, or better yet the orange degreaser, sold is about the same as a car wash spray or two anyway and a gallon will go for a long time. Get one of those one gallon sprayers and you will be set for life.