I have tried everything to save the unused caulk left in a tube: caps, plugs, nails, tape, wire, even those little rubbers you roll on the tip. Inevitably, the caulk in the tip of the tube dries out and leaves all that good material unusable inside the tube. Here is a way to clear any plug from the nozzle without cutting it down to a nub.
First, cut the head off the longest decking screw you can get (4 in. to 5 in. works best). Shorter screws work as long as they can reach past the plug, but you will quickly find that it is not good to have the chuck of your drill loaded with silicone. Use a long screw, or push the screw through a piece of cardboard to shield the chuck. Now chuck the shaft of the screw into your drill. Load the tube into your caulking gun, and drive the screw into the end of the nozzle until it is past the plug. Start squeezing the gun to put pressure on the plug while you spin the screw.
As you pull out the clogged material, start to rotate the screw around to scour the inside of the nozzle. Keep putting pressure on the gun as you go until the tube runs as freely as you need it to.
Will Stark, Shutesbury, MA