Small bottle-cap adaptor allowing connection with two 6mm ID hoses by using M5 hose couplers (Earlier versions printed the coupler, which had bad results). Cut two M5 threads in to the top in- and outlet, as well as a M5 thread into the pipe adaptor, where you have to screw in an M5 brass or steel pipe.
I've included multiple versions of the STL. Take a look at the CapAdapter.scad file and change the parameters as you like.
Also, use an O-Ring to seal the cap to the bottle, or use the original seal of a bottlecap with two holes cut into it.
This project includes the Universal Hose Coupler & Funnel Maker (CC-BY-SA), the Necks & Caps for DIY projects (CC-BY) and the OpenSCAD threads.
This thing has been designed for use with my Arduino-controlled cocktail-machine.