Once The Toothpaste Is Out Of the Tube

Since Bin Laden has already won the war against western society, with TSA limiting liquids & pastes we can bring on planes to less than 3 ounces - not to mention taking off your shoes, having your genitals felt up, and not being able to take cork screws onto aircraft - we've gone through lots of little tubes of toothpaste in our home.  Since fluid dynamics works, and I got a B+ in Fluid Dynamics back in college, and the tooth paste manufacturers conveniently use the Same Size tube openings on virtually all their products (thanks to common, high volume, injection mold tooling and physics!) I've found that it IS possible to REFILL toothpaste tubes.  Whoever has said that "once the tooth paste is out of the tube, you can't put it back in" has never tried this before.

It's very simple actually.  All you need are opposable thumbs, adequate hand strength, hand-eye coordination, one (or more) empty tubes of toothpaste, and one much more full tube.  Align the empty and full tubes, making sure both opening are concentric.  Hold them together firmly, and squeeze the larger tube.  Viscous tooth paste will flow into the flattened smaller tube, with no excess spillage.  Perfect alignment pretty much guarantees that you're not going to waste any.

Once you've nearly filled the smaller tube, back off on the compressive pressure on the larger tube.  Relax your squeezing grip and allow the pressures to equalize.  A small amount of back-flow may occur, but that's fine, since you have not separated the tubes yet.  Once pressures equalize, move the tubes in a shearing motion, 90 degrees opposed (not a tensile motion, pulling them apart) and then re-cap each tube.   I know this works at least twice on the same tube, but I've not conducted LCF (low cycle fatigue) tests to see how many dozens or hundreds of refills can be done this way.  Eventually, I suspect the smaller tube's rigid end cap will start to separate from the expandable tube, after the 4th or 5th refill, since it was originally designed to last only once (without rupturing) and the be discarded - but maybe there's a large safety factor build into tube design - I don't know.

I do know, that finding sensitive tooth paste mini-tubes is not easy.  Everyone carries whitening mini-tubes, sure, but the sensitive mini-tubes we got from our old dentist in South Carolina, and obviously traveling back there to get mini-tubes is impractical  =)

I agree that "once the tooth paste is out of the tube and on the floor / in the sink / on your tooth brush, it is hard to put back in the tube" - yes indeed.  But transferring it from one larger tube to a smaller traveling size tube, is quite simple.