Sounds like your friend is getting a great deal. A bleach + strong soap mix is great for this and many boat owners use this sort of mixture. Marinas may or may not have regulations about water pollution in this way near you, so could be worth a google.
There are many biodegradable detergents available if you are especially concerned about pollution. You can find these soaps in regular supermarkets these days. Raccoon poop is nasty but not all that difficult to clean off.