Up where I live (Scotland) there is a chain of car wash places called Autoshine Express, not sure if there national (yet). They use a detergent on the bodywork that seems to be pretty good. They dont use anything to agitate the soap on the car, they just apply it with a lance, leave a few mins while your in the queue and then pressure wash off. While you are waiting you can see the colour of the soap changing colour as it starts absorbing the dirt.
Has anyone any ideas what they use, or can recommend any other detergents for application using a pressure washer that dont need any agitation using sponge/brush etc so there is little or no contact with the bodywork.
Thanks
Steve