I gather the complete vehicles can't be sold on for human rights reasons, but I wonder if the scrapyard would take an order for just one of the water sprayer mechanisms for wetlook use?
I'd love to see someone buy one, redo the entire body of it, and fill it with gunge for a rave party. Yes, I think that is the BEST possible fate for these vehicles.
Go with a pressure washer, or semi-trash pump for substances that have a high viscosity. It wouldn't be too difficult to engineer a tank for portability.