Oh, You make me blush.
It depends on the type of car lot that you are doing, sort of. If it is a dealership, then DI water and a guy or two to dry will do the trick. If it is cars taht get used on the road, I.E. Phone company, Power company, City governement, etc, then the method that Ron described to you works really well. If you do use a good quality soap then even if it dries, as long as you don't let it set too long it will come right off. I use Zymol from Price Club for this. I am not normally one to do the discount club thing for my wash products, but someone recommended this to me, and it works excellent.
Scott Stone