I was in Oklahoma City last week for a meeting, and in the underground parking garage I noticed two stalls had been converted to car wash stations. If you wanted you could pay to have them wash your car while you had it sitting in the garage and you were in the building.
Their stations looked to have a hose hooked into the fire sprinkler water system (the floors already have drainage.)
I have seen car washes and oil change at airport parking (Fine in Tulsa does this), but I had never seen it in a nondescript parking garage in downtown.
Shows there is always a way for a creative business idea to get started.