That's what I call being dedicated to doing it right! There is another member on this site that is equally into detailing, he had pointed out that a Kranzle power washer is the way to go. Its not a Home Depot unit, only sold by authorized dealers. From what I have found price wise about $1700.00 will get you a K2017 is 1600 psi and 1.6 gpm freeze proof, high pressure soap delivery and a hefty weight of 90 lbs
https://www.kranzleusa.com/k2017-k2020
I have a friend here in NJ that installs custom car,truck,bus, while vehicle is parked, the car wash system is mobilized to go from front to back and then blown dry and finally finished up by hand. They have done several installs inside garages that were set up to drive through, undercar spray systems to remove the dreaded road salt and brine that loves to eat metal.
He made a small U shaped unit that he uses in his driveway with 40 degree nozzles pointed up and 2x4`s along each pipe so that they do not get crushed when he drives over the set up. It is hooked up to his Dewalt gas powered power washer with a quick connect. It does work awesome and breaks down into 3 pieces for storage
They started out doing one for Academy bus service which is a major public transportation service along the east coast and they have over 1000 buses to take care of, and it's all done inside one building. Steam clean for the engine bay and a water purification system that is huge. They also have to filter the water that is used to wash the engines before it can be returned back into the system for reuse on the engines only.