I was browsing Printables and found a library for bottle threads called PET bottle PCO28 1810 thread standard models by steffanders.

There should be a silent-yet-obligatory rule in the community that any time a new bottle cap threads library comes out, a vortex bottle generator needs to be created with it.

https://youtu.be/5tYT9fEJzMc

Printing

It can be made with PLA, but PETG is recommended. In the video, PETG is used.

There is a version with support built-in and one without supports. The outer support ring connects to the cap's seal ring - make sure not to damage the seal ring (although I don't think it's possible to do so by accident unless you get carried away using violent force).

Parts

This thing also requires two 2-liter bottles that use the standard cap threads. In the video, Diet Coke bottles are used because of their clarity.

Assembly

1. Tear off labels from the 2-liter bottles
2. Fill one of the bottles with 1/2 to 2/3 full of water.
3. Optional - add food coloring and fine debris (i.e., glitter) to the water.
4. Screw on the coupler (this thing) to the bottle with water.
5. Screw the other bottle on the other side of the coupler.
6. Make sure the two bottles are fully tightened to the coupler.

Usage

1. Turn the assembly so the side with water is at the top.
2. Gently swirl the assembly from the top and lightly and repeatedly squeeze the bottom to pump air upwards.
3. When a vortex is fully formed, stand the bottle and let go of it until all the water has drained.
4. Rinse and repeat.

Caveat Emptor

The cap design that I remixed from is advertised as watertight; in my experience, it has been. I can't vouch for water tightness for everyone and their setups, but if it's not, then it should only leak minimally.

Also, while I don't expect this object to ever physically fail, be careful, and don't forget it's a 3D-printed object filled with water.