Since you're only talking about one short section of water line, if you buy the fitting you could use a bicycle tire pump to push the water out of that short section of water line. Or, you could buy the pump lynnmor suggested, although he didn't provide a link. Another idea would be to hook a beer bong up to a short section of garden hose and pour the antifreeze in the water inlet, then after a careful rinsing, you'd have a recreational toy for campfires.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI