Hi Gang: When I travel I like to take those small travel size tubes of toothpaste. I do get a few "free" from the dentist. But to buy them is almost as much as a big tube! So I would fill them by pressing a big tube to an empty small tube. Often I would make quite a mess. So I thought: what if I had Coupling Caps to hole the tubes together.
Step 1: Collect Tubes and Caps
So save up some empty tubes and their caps. Please note the caps come in two sizes, 1/2" threads and 9/16" threads. 9/16" diameter seem to be more common, and usually have flip caps, which are really nice when you travel.
Step 2: Poke Holes in the Caps
The plastic the caps are made from is easy to poke holes in, so you can use a knife or use a real drill bit, both work fine. Clean up the chips and rinse out the old toothpaste if any.
Step 3: Holes Finished
Not real pretty holes, but they will work even if they are not perfectly round.
Step 4: Connecting Sleeve
So we can glue the caps together, and it is easier if we have a sleeve to hold them straight while the glue set up. I used a pudding cup and cut a strip from the side.
Step 5: First Cut
Here I have cut the rim and bottom off.
Step 6: Trim Strip to Size
So guess at the depth of the recess in the two caps and cut a strip about that width.
Step 7: Roll Strip Into a Sleeve
Once you have the strip cut size roll it into a tube so it can slide into the recess in the top of one cap. Then slip the other cap on too.
Step 8: Ready for Glue
Solvent glues don't hold this type of plastic well. So use Epoxy Glue. Put the two caps together with the sleeve and you are ready to mix your Epoxy Glue.
Step 9: Wait for the Glue to Harden
So put a good coat of Epoxy Glue all around the two caps and then wait. Epoxy sets up fast, but it is best to wait over night. Here is the finished Coupling Caps.
Step 10: Ready to Fill a Travel Tube
When the Glue is set you can fill a travel tube. Screw a big tube to one end of the Coupling Caps. Smash all the air out of the travel tube and screw it to the other end. Then squeeze the big tube. The toothpaste will flow to the smaller tube and you will see it inflate! Don't overfill it or when you take the coupling caps off the toothpaste will squirt back out.
Step 11: All Finished!
So let the pressure equalize, unscrew the tubes from the Coupling Caps. Put regular caps on the tubes. Wash the left over toothpaste from the Coupling Caps so they will be clean for next time. I usually do several small tubes at once. Then I have plenty for a bunch of trips.
Good luck and Bonn Voyage!