Bottle Whirlpool Vortex

My kids were asking about Cyclones and Vortexes so I went about finding a bottle joiner to show them the classic vortex-in-a-bottle trick.
I tried a few from Thingiverse but wasn't satisfied with any.
They always leaked and broke.

I have designed this to be simpler and to accomodate a washer in the middle that ensures an excellent seal between the two bottles. If you don't have a washer or some TPU filament to print the one I have supplied, then you can just screw the bottles in together and they seal pretty well onto each other. If you have some flexible filament (eg TPU) then you can print the supplied washer and place the washer in the middle of the joiner and there will be no leaks :-)

Just fill a bottle with some coloured water, attach the joiner and then attach another bottle of the same size. Invert the bottles and give them a swirl. You should see a nice vortex as the top bottle empties into the bottom one!

Note, you might have to remove the little bit of the old lid