After poking filament through pieces of sponge, I finally printed this out and it works better. Being a split sponge holder you can monitor how dirty the sponge is getting every time it is opened up while starting a different spool. On my 1.75mm filament I've found that two pieces of sponge 14x20x6mm fit almost perfectly in the holder.
Prusa (Filament PM - Plasty Mladeč) PLA
Printed with the bottom layer hilbert curve fill pattern. Gives a 3-D, almost holographic, visual texture while feeling perfectly smooth.