This is a fun kit to experiment with. Fun and educational for kids and adults. You'll need 2 plastic bb:s (for soft air-gun 6 mm dia) and a piece of pvc-pipe (id 17 and od 20mm). A piece of 8 mm dowel and some tubing with an id of 8 mm. Two suitable o-rings for the piston, some grease and some hot-glue (for pipe bottom and top). Look at the pics, they explain a lot. The source files (freecad) are provided so you can change dimensions to be able to use the stuff your empire of dirt provides. We used some cable ties to prevent leakage.

And there's more than one way to build a working pump with these components!