I have an enclosed printer that places the spool inside the chamber. It's great for keeping things tidy and keeping the spool dry during a print. However, it is complicated to change filaments during a print (the plate gets in the way) or to print from a dry-box (larger spools) without opening the door, which is less than ideal.

It may look angular, but the bore is a gentle curve from one end to the other, with a non curved bore for the other side. The i.d. of the channels is 4 mm with a tapered ramp to the shoulder of the tube.

This is for a reverse bowden setup, I would not suggest pushing through this Y as it is bored out for less friction. The ends are press fit with a 1% draft for 4 mm o.d. PTFE tubing, they should fit snugly at full depth (15 mm).

Mine was printed in ABS due to the chamber temperatures I run at, but PET-G or PLA should be fine for non-heated chambers.

For best results, print on the wider end, no supports, on a non-bed slinger (or just print slowly).
I did not try it, but it should work without support printed on one of its flat sides.