This basically is a dust scrubber that removes dust and other particles from the filament as it goes thru the sponges. Normally this dust could potentially clog up the extruder nozzle or break something.

Story:
After one night of printing, I discovered a large dust ball inside the extruder just before the idlerwheel. After a disassembly I found more. Apparently I had thrown the filament spool in to a really dusty area and dust got sucked to the abs.

About pictures:
At the first picture top right is the dust that gathered to the temporary scrubber while these parts were extruded. (black stuff)
Lower right is the way the sponges are placed in side the cup. (10x10x20)x4

The second photo is installation pic (it clips on to the extruder).

Due to my not-so-good blender skills the skeinforge is going to whine something when the cup.stl is processed but it's going print out mostly ok (one weird solid layer middle of the cup but it's easy to remove).
Because of that I have included the blender file where you can tweak the object relations if needed.

Other than that, just print, clean and assemble (you can use either filament pieces or M3 bolts).