| For goodness' sake, don't use a sponge - those things are made to inflict scratches on your car!
Use a lambswool or microfibre noodle mit, and two buckets - one with the shampoo in it, a second one for rinsing the washmitt out after doing each panel of the car.
Frankly I'd steer clear of all the automatic car washes, and any handwashers staffed by eastern Europeans with sponges and dirty chamois leathers. | 
