Although this was designed from scratch, it was definitely inspired by
edmo's 2 liter bottle watering spout. Since I water my plants with a gallon jug of spring water instead of a 2 liter bottle, I wanted an adapter that would fit that.
Printed on an Afinia H479 oriented upside down. Avoid using support material if possible because the threads are difficult to clean up otherwise.
Make sure you poke a small hole in the top of the handle to act as a vent, or the water will have trouble pouring out when the jug is full.