A teapot will dribble, or otherwise not pour correctly if the shape of the edge of the orifice is incorrect. Usually, a sharp edge pours best, and this means that the spout, at least, should be made of metal.
If the lip is too fat, the tea will actually run around the drip down the spout.
The same principle is applied in roofing. The sharp metal drip edge, when correctly installed , will keep the rain from actully running back up the bottom of the edge of the roof, and eventually rotting your sturcture. It took me a long time to figure out how the drip edge works, and it seems many contractors have never learned that secret.
MD