Customisable Bottle drainer

This is a gadget to connect two bottles together, so you can drain the old one into the new one and so get the last of the product out, or drain the new one into an old one becasue you like the old one better.

There are lots of designs for such things on Thingiverse, but after trying them out, I decided I wanted to create my own:
- I didn't want a threaded connector. It can be quite fiddly trying to screw two large bottles together, especally when one is upside-down. Besides, some bottles don't have threads, just snap-on caps.
- On the other hand, I didn't want just a push-fit. When the top bottle is full of liquid, and it's slopping about, it's too easy for the bottle to pull out of the adaptor.
- I didn't want a simple funnel. I wanted to be able to leave this overnight.

(I did find a design which I quite liked, of which this is a derivative. But I'm afraid I lost it again. If I find it, or if you find it and tell me, I'll credit the original author.)

This design is