Featured in Make Magazine's Winter 2013 Ultimate Guide to 3D printing!

This is a watering spout for a 2L bottle or anything that can screw on to soda bottle threads. There is also a Autodesk Inventor file attached that has no threads, so you can adjust as you see fit.
The point here is that, thanks to the wonders of 3D printing, you can repurpose what would be a piece of trash into something useful. This spout would be useful for seedlings or other small plants that require measured amounts of water. Also, this watering spout has 1/8" thick walls. You can't buy something this durable at the store!
I've recently (May 2013) uploaded a modified design file that takes care of some sealing issues and adds threads to the bottle. I added the threads in with an assembly, so the STL file got a lot bigger in the process. It prints great, though. If it still leaks, try taking the rubber gasket out of the 2 L cap, drilling it out and using it as a washer.

Derivatives:
ljudmila changed up the threads:
http://www.thingiverse.com/thing:10600

Chickan put this on a watering hose:
http://www.thingiverse.com/thing:95723

chickan also made one with different threads:
http://www.thingiverse.com/thing:95209

uumeran adapted it to a milk jug:
http://www.thingiverse.com/thing:124873

CaptKirk made it smaller and more efficient:
http://www.thingiverse.com/thing:315394

steveweber314 turned it into a low-pressure garden hose nozzle:
http://www.thingiverse.com/thing:368595

Sylvain3D added a handle and made a few modifications to the nozzle:
https://www.thingiverse.com/thing:794110

mraiser put it on a kitty litter jug:
http://www.thingiverse.com/thing:916767

zhinker put it on a US milk jug:
https://www.thingiverse.com/thing:2320492

Don't have a 3D printer but want one? Message me and we can work something out. :)

I'd recommend running this through the dishwasher before you water your plants with it.