Most people think that the obvious answer to dealing with these chemicals is to take the car to the car wash in order to remove the substances.
This answer is only partly correct. Obviously, you want to get these chemicals off of the car as quickly as possible. The problem comes in the form of the car wash itself and its design.
If you're going to an automatic car wash, the very design of it has a tendency to grind the chemicals into the finish of the car as opposed to getting rid of them. When you see those big machines coming at your car that rub it with soap, they're actually grinding the impurities right into the surface.
Manual car washes are a better option because you can spray the entire car down before you allow anything else to touch it.
Once you've done that, you can take the foam brush and make sure that it's really clean but you have to be meticulous in order to make sure that everything has been removed. Your best bet is to take the car to a manual car wash, spray it off from bumper to bumper, top to bottom, and then use the foam brush on it so you can wash it again. Once you've done all of that, you can go to an automatic car wash and have the undercarriage sprayed down.