A friend and I installed a seperate windshield washer system in his car and had a hidden spigot under the dash. Get a softdrink at the drive in,hold it under the dash and push the button!
Heh, that's outstanding. I had a '73 Pontiac Grand Prix that had a large, deep spare tire well in the trunk. We'd move the spare and pull the rubber drain plug down there, then set a pony keg in the well with several sacks of ice. The tap hose was passed forward through the rear seat's folding armrest cutout.
Reminds me of my former father-in-law. A relative always gave him a bottle of Rebel Yell for Christmas every year. Real rotgut whiskey. He would use it as antifreeze in the windshield washer of his car. It reeked terribly; you wouldn't want to use it around a cop.