Caulk is – in the grand scheme of things – pretty cheap. Still, there’s no point in wasting it, especially when you crack a new tube and only use half of it. SawmillCreeker David Klug asked “When ever I use a caulking tube I rarely use all of the material in it and when I want to use it again sometime later it has become hard and I have to throw the tube away. Is there any way to seal it so you can use it later?”

There are some great responses from the Creekers – where appropriate I added pictures that link to the stuff they’re talking about:

1) water proof wire nuts
-Roger Fitzsimonds

2) Buy a toilet wax ring ($1) and push the tip of the calk in it when done. the wax seals it up and so far I have not lost one tube of calk.
– Lloyd Brown

3) Duct Tape. Take a piece about 2″ long, and place the nozzle end in the center, both width and length, of the sticky side. Then just fold the tape down the long sides of the nozzle. The two sticky sides will come together. Then go back and press the tape closely around the entire nozzle.
-Ken Garlock

4) Recently I bought some little , well for lack of vocabulary little condoms, and they seem to work pretty well. I think it was Lee Valley that had them.
-Roger Fitzsimonds

(note, they’re commonly referred to as Nozzle Caps. Nozzle Condoms certainly seems appropriate though…)

5) a simple solution is to use a 16d penny nail just push it into the open hole and then put some duct tape around the opening.
-Ron McNeil

6) A golf tee works nicely
-Mark Hulette
(note – a golf tee probably isn’t going to last you that long but it’s better than nothing!)

Some other tube sealing resources that reinforce the above ideas:
How to Seal a Used Caulking Tube
How to Save Leftover Caulking

Other “Great Ideas” Posts:
11 Ideas for Wood Cut Offs
Table Saw Blade Storage
11 Cheap, Recycled or Free Items Useful in the Wood Shop
Seven Ideas for Drill Bit Storage
5 Tips for Removing Wood Glue from Your Clothes
Getting Sheet Goods Home: 9 Ways to Reduce the Pain