Print the rack too...
The Straw Pipette:
"Print the upper body, lower body, plunger, and two thumb gears. You will need a spring, which I got from a kids Pez dispenser for its form factor. The balloon membrane is elastic so you may get away without the spring but it is nicer to have it. You will also need a balloon, some tape, and a straw. It is designed for one particular straw diameter but I can upload others if there is demand. See the attached photos for assembly steps. I printed all the pieces at 0.1mm with 15% fill and 100% fill for the plunger."