For printers that use a tube to control the filament path to the extruder, this part allows you to put a filament path directly on to the start of the tube. Once printed, feed some sponge into the bottom hole with a drop or two of oil. Push some filament through initially to get the filament path through the sponge started, then push fit to the tube on the printer.
The initial design here is for the original feed tubes that came with the E3D Bigbox. The model is parameterized, so if you want to alter it, the model is online here:
Nothing complex required in the printing process