Now I am using Varsol, $4.00 a gallon 4/5 parts
Gunk Concentrate, $16.00 a gallon 1/5 part
For the really hard grim, soil that has been in place for a year or more, it still requires using a rag with the VARSOL and GUNK mixture but for most of it I can simply spray the Varsol/Gunk mixture on using a pump up pressure garden sprayer, [they cost $28.00] and then washing it off with the hose. I do not know where to buy an atomizer. That is what we used to use before the FBO moved off and took it with him. The atomizer used the shop air hose and would blast the bottom of the plane with Varsol.
I tried using a high pressure washer and it did not seem to be any better than just using city water pressure.