simple green is all I use, generally if its really bad I mix in a few cups to a 1 gallon garden sprayer and spray down what im cleaning, let it sit for 10 minutes or so then hose it off, even stuff like exhaust soot comes right off, also ZEP spray bottles with 50%% simple green, and spray it on for the tougher stuff
plus its 100% safe, no chemical burns and won't kill plants, unlike the super clean I won in a giveaway, stuff ruined one of my shirts and burned the back of my neck with a little overspray