A simple handle you can screw on a 1.5 liter soda bottle or similar.
I made this for my mother because her hands hurt and sometimes it is difficult for her to pour from the large bottles.

I can print this without supports, but depending on your cooling, you might need supports.
Print with at least 4 walls.

EDIT!
Added a version that might be easier to print without supports.

EDIT2!
Made the opening on the end thicker so to make sure it is waterproof and added a model for a gasket(print using TPU) that goes between the bottle and the model.
Tested and it works!