As you know, the cartridges they use countdown to register the filament use and signal the end; like the DaVinci...when the countdown is hit, or when there is not enough filament left in the roll for a particular job, then many suppliers just send them back for the official re-filling.

A local supplier in my area (who knows I have a printer) asked me if I was interested in the spare filament as he yanked out nearly 9 meters of ABS and handed it to me.

He said he will empty all of his cartridges in this way, and for me to just stop in from time to time to pick it up!

Pretty sweet deal...