Most homebrewers are familiar with fermentation going wild, and foam erupting from the fermenter. The situation is adequately handled by a blowoff tube into a bucket of water or sanitizer liquid. After a few days things will be more calm.
However, if you have a digital airlock like the Plaato, you want to count all the bubbles and keep track of the fermentation process. This little device can be fitted on a standard plastic can and allow for in- outgoing traffic. In the outgoing lane you mount the airlock. A 12mm ID hose is suitable for the airlock mount, for the internal piece from the cap to the bottom and from your fermenter to the cap.
You need to drill two holes in the plastic cap to be able to fit the insert in it. You probably also need to adjust the hole size in the insert where a 12 mm copper pipe (or similar) goes in. A 12 mm drill bit does the trick.
The base plate is only 1 mm thick and hence not so strong, but thicker plates could make it more difficult to fit. The threads on these plastic caps are short.
Some keg luge on possible leakage paths will help you keep things airtight.
Well, it worked for me, and I hope other will be able to use it as well.
Feel free to modify it for your setup, and possibly make a complete cap with threads (I couldn't find the thread size).

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