Lots of these to go around, here's my take. Fits PTFE tubing commonly used for 1.75 mm filament (4 mm outer, 2 mm inner diameter). The front part of the PTFE fitting base is threaded with DIN pipe threads, and fits these connectors:

https://www.aliexpress.com/item/10PCS-Pneumatic-Connector-PC4-01-1-75mm-PTFE-Tube-Quick-Coupler-Feed-inlet-For-J-head/32808622940.html

The purpose of the inner funnel is to avoid sharp bends if the filament isn't fed completely straight into the hole. This part can probably be omitted.

All screw holes are M3. You can use hot glue or window silicone to make the installation air tight. I used a thin neoprene tape gasket to seal the lid.

The box used is called SmartStore Home 16, and the spool holder bracket is angled (86°) to fit this specific box. The tube used as spool holder is a 25.5 mm thick steel pipe a had lying around.

UPDATE: Added a stopper to prevent air from leaking into the PTFE tubes when no filament is loaded.