This part is for used together with "Bottle Connector with funnel by cgongora69" (http://www.thingiverse.com/thing:902607) to maintain nutrient solution level in sprout tray at 5-6mm or 12mm height. ** UPDATE (6 Sep 2015) : I've added the 12mm version. Recommed to print this version if you use sponge as grow medium.Print with this setting. 0.2mm, 15% infill 2 shells. Fill 500ml bottle with nutrient solution. Put the Bottle Connector cap to the bottle and place it bottom up onto the refiller. Make sure that you've already put some nutrient solution in sprout tray before you do this. By this way it will create vacuum inside the bottle. When nutrient solution is down below the cap, it will drain out some solution to refill the tray automatically. Likely the pet's automatic water refill tray.