There's actually an easy way to refill those dollar store Scripto lighters! Take the fuel tank out, open the regulator a few turns, and hold it open while pressing a butane can onto it. Fill it about 3/4 full, twist the regulator back down to normal, and it is good to go ...
Zippo Lighter Fuel Fluid 4 oz (118ml) - 6 Can - Walmart.com