Aside from the obvious jokes that this topic always brings up...
I put 2oz of viper restore (acid tile and grout cleaner) in a cup (undiluted). Dip a corner of a small terry towel in it and just wipe/rub the dirt away. It will make it look brand new shiny!! Once you finished, spray a shot of your prespray on it to neutralize the acid and wash it down with water.
This is the single best way to clean up a dirty wand! I have done it tons of times. Even showed it to other cleaners in town, that would be scraping scratching polishing the wand and wouldn't come clean as my method would make them do.
I don't think having the wand in an acid solution all night is such a great idea (even if its a mild vinegar only). How would it affect the wand and- if there are- checkvalves and such.