Update May 2020: One of the three fittings I have in use broke. My guess is that the PLA became brittle under constant water contact. I'll try ABS or PETG soon. Do not print this in PLA!
Bulkhead fittings are expensive where I live, so I made my own. I have versions for 12mm (1/2") and 6mm (1/4") ID hose. More may come in the future. Needs an O ring with ID 17mm and OD 20mm. I recommend a 16mm drill for installing the bulkheads.
Added 9mm and 25mm fittings. The 25mm version needs an O ring with ID 34mm and OD 41mm. I haven't tested these two, so please use with caution.