I don't know if this is "best" and may not be "easily done" but you may just want to try some paint remover or more specifically citristrip and then brush it off (with one of those long handle, stiff bristle garage floor type brush) after it has sit after more than the recommended time. Also try one of the deck cleaners that you just spray on with a tank sprayer and a brush. It requires elbow grease which many people are allergic to but you don't have the mess of a power sprayer which gets stuff all over the side of the house and in the yard. No method will keep stuff off the ground underneath if that matters but this may limit that.
I also prefer a sponge/rag and soap bucket when washing a car cause the pressure washers still leave dirt but at times when I'm low on elbow grease, it's car wash time and then it splatters on my clothes. Good luck. Post back with what you do and how it worked.