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 fully-customisable: you can change the diameters of the top and bottom pipes (that insert into the bottle necks), and the angle of the funnel. If you want even more control, you can change the wall thickness, and the pointiness of the profile. If even that is not enough for you, then the code should be pretty-well explained.

We now have a selection of these in different colours in our rubble drawer: different sizes, some to connect large, bulk containers to smaller ones, and an adaptor to drain liquid soap into a hand-made ceramic dispenser.