Although the first car wash appeared in 1914, it would take a few decades to figure out the best way to go about it. Since dirt roads were the norm back then, the car undercarriages would get extremely dirty.
One solution was a flooded circular basin, such as Chicago’s “Auto Wash Bowl” depicted here, in 1924. The cars were driven around, and then detailed by hand up top. (via Findery)
"Trudy, aka Firestar, had her hands full trying to politely shake off the roaming hands of Roger McDowell, who followed her like a stray puppy and persistently tried to pick her up…. My initial poses—signature Webhead moves—were quickly shot down by the photographer. His ‘vision’ included Spider-Man clutching the knob of a baseball bat, held upright between his spread legs and grabbed by Lee Mazzilli and Wally Backman."