You probably don’t use caulk that much, and when you do, always have some leftover. To seal your half-used caulk tube, you’ll need a plastic milk container and a lighter or candle. Cut a circular piece from a plastic container that’s 1.5 to 2.5 inches in diameter. Clean the nozzle of the caulk tube. Position your heat source at the center of the plastic piece and move it in a circular motion until it becomes transparent. Apply the plastic over the tip of the caulk tube. The melted plastic will secure itself and harden. Add a piece of tape at the bottom of the plastic top. And the next time you need it, you won’t have to buy a new tube of caulk.