Parts I purchased:
1) Very fine colored sand (hobby, craft store, Amazon).
Print and assemble all pieces as shown in "Assembly.skp". After printing, remove the hold down tabs from "Hopper.stl" and "Pivot.stl".
Test fit and trim, file, sand, etc. all parts as necessary for smooth movement of moving surfaces, and tight fit for non moving surfaces. Depending on the colors you chose and your printer settings, more or less trimming, filing and/or sanding will be required. "Pivot.stl" must move freely on its axle.
Assemble as shown in "Assembly.skp".
Comment if you have questions.