Only two STL's are required. One is optional and can be used multiple times in the over all case. One is just for full display of what it looks like all together, not for printing.
Bottom.stl - REQUIRED - Contains the Carbon Pellets that can be found on Amazon: https://www.amazon.com/gp/product/B01F1QZTQC/
Lid.stl - REQUIRED - snaps to bottom or mid section.
Mid Section.stl - OPTIONAL - Snaps to the bottom and the Lid can snap to the top of it.
Filter Case.stl - VISUAL - This is just a 3d of it all together.