I’ve used nails, pencils, dowels, and even packing tape to try to keep my glue nozzles clear, and none consistently work; when I try to use them again, the tube is soft but the nozzle is solid. The Twist-n-Seal Stopper forms an air-tight seal on plastic nozzles by tapping threads in the malleable plastic. The threads will withstand 40 lbs of axial force so it won’t pop out. The glass-reinforced plastic plug is non-stick and is removed by unscrewing from the tube. The top is flattened to stand upright when removed, keeping things clean on your workspace. You can find the Twist-n-Seal at Lee Valley for $3.20/pkg of five.
Twist-n-Seal Stopper [Lee Valley]