CO2 Flipper for fertilizing fish tank plants.Print without support and rasp the outer edge plain to let the bubbles run smoothly. Guide the tube through the hole, then through the clamp and fix the clamp in the fitting of the inner side of the flipper. For the cover I used a stub of a PET soft drink bottle with a approx. diameter of 60 mm or scale your print accordingly. The PET stub should have no profile. Use a hair dryer to shrink the PET cover and it will tighten the flipper so no bubbles will escape through the edges. See it here in action: http://www.youtube.com/watch?v=dfQ7tZzYggw