Filament waste is going to be a big, big problem for practitioners of 3D printing, especially hobbyists who see it as money going from wallet to scrap bin.

The simple answer is to obtain a filament recycler like Filabot (at $US1340 for a recyler and grinder), or to study various designs published on the Net and cobble something together from stuff scavenged from a junk yard. You just have to stockpile your filament waste and process it every now and then, like you do with aluminium cans.

(PS. I have no affiliation with the people who make the Filabot)

Old Man Emu