Coke (PET) Bottle Tornado Coupler

This is a coupler for joining two soda bottles to make a tornado (reference: https://www.wikihow.com/Make-a-Tornado-in-a-Bottle).

There are three models:

• Coupler, short—use this on its own, and tighten the two bottles to each other.
• Coupler, tall—use this with the reducer.
• Reducer—use this with the long coupler to create a smaller opening for a different tornado effect. Print in flex. It's a tight squeeze to get it into the coupler, you might need to use a C clamp and some elbow grease.

It's impressively less leak-resistant when used for tornados. If you squeeze the bottles to create pressure while there's liquid over the coupler, well… that's another science experiment.

Update 2023-03-13: There is a new r3 version of the coupler with an added grip (thanks Onboard4970 for the idea!)