Unused Caulk – There actually is a way to save the unused caulk left in the tube, rather than tossing it out. You can always try to store your cartridge for later use using a plastic electrical connector as an easy way to quickly seal and reopen the tube. If you can’t find a connector, place a 2-inch nail into the end of the nozzle, then wrap the entire nozzle tightly in plastic wrap or aluminum foil. This will help keep the caulk in the nozzle from hardening for use at a later date, but the very best idea is to use the wax from a wax toilet gasket ring (you can buy one for about $2.00…. and one will last you almost forever). Put the wax in a small container, like a router bit case with a top on it, this keeps the wax from getting all over, and the wax case is small enough to put in your tool box and take it with you. After you caulk something and have some left over, just push the tip of the caulk tube into the wax (approx. a couple of inches) and it seals the tube closed. Later, when you need to use your half used tube, put it in your gun and squeeze out the wax and you are in back in business with no waste!
Just another expert idea from Guy Calor, the Caulk King and CaulkWarmer