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A few 3D printers have an option in their controller menu for unloading and loading filament. Just before you start loading/unloading, then be certain that the extruder is not already loaded together using all the filament. If there's filament in the extrusion mind, remove it first. If http://zilla3d.com/ZillaGrip-Cold-3D-Printing-Coating-_c_20.html has an alternative for removing the filament, put it to use and then watch it until it unloads out of the extrusion head.