Originally Posted by THE TECH
I would shy away from anything but a wash especially when it comes to the rear bumpers since many of those contaminants are likely from the engine/exhaust.
Nailed it. It's funny cause detail sprays advertise as something to be used between washes to basically keep the car looking its best but you will definitely introduce swirls into the paint. Use it after a wash as a drying aid and to add some gloss and slickness as well