WD40 is a decent penetrant though right? Would it make any sense to spray the whole freaking thing with WD or even the cheap walmart lubricant version of it before you wash it, just to penetrate the dirt/rust/corrosion/oxidation and help "lift" it all away? Then the usual soap cannon, pressure wash, and then hand wash?
Ive been using a fair amount of the walmart "lubricant" on my 40 as Ive been bringing it back to life, and Ive thought about literally just spraying the entire exterior down with it. As others have said, its pretty thin, (the generic walmart version is even thinner I think) so its not hard to wash away.
To be clear, this is not for any sort of protection or rust prevention, but for the initial cleaning.