3d printer filament wipe

Insert a small piece of ptfe tube into the 4mm hole, pre-extruder.
Thread your filament in from the large open end, up the ptfe and into your extruder.
finally pack some sponge/tissue into the large opening once the filament is loaded.
Check/change the sponge every few prints to prevent a build up.

This design is intended to reduce the amount of atmospheric dust/debris being drawn into the throat, extruder assembly and the nozzle.