How to properly wash your 370 w/o damaging paint? Help

1st

I have been to these places when I had no house and lived in an apartment. There ok but dangerous because of contractors. My process was as follows 1. Use rinse function to get all the dirt off your car 2. Use the soap through the hose function hose down the car 3. Use my own mitt with my own soap and soap up the car 4. rinse it. Never used the wax through the hose or that nasty brush. Also when I say dangerous because of contractors is because I have noticed that at these places even though its posted not to rinse off muddy cars/trucks. Contractors tend to go here after a job and rinse causing nails that where loose in their beds to go on the ground. So yes I have picked up nails in my tires here and there. So what I used to do is before going in the bay is get out and inspect for screws, nails, debris then enter at my own risk.