Have you finished a caulking job and discovered that you still have a significant amount of caulk left in the tube that you don't want to waste? This simple tip can preserve that unused caulk... at least for a while.
Take an electrical wire nut and simply screw it on the end of the caulk tube.
This technique works well for glue bottles and even containers that hold the chalk dust for a chalk line.
Wire nuts are available in different sizes indicated by different colors. If the first size doesn't fit, just try another one!