I picked up an item at the supermarket Intended to be used to wash dishes. It has a hollow handle with a sponge on the end. I fill the handle with undercarriage spray, put the sponge back on and "paint" it in my wheel wells. Hasn't dripped on the garage floor or driveway yet. Or you can just spray the sponge and apply it that way. No way am I finishing a car without undercarriage spray.