Watering Can Spout

The inner diameter is about 25mm at the base and tapers to 22.5mm, at 36mm of length.
There's a small ridge inside the tube (at 20mm down the length) that helps hold it on to the watering can.

I printed in resin and softened it by warming in hot water to get that ridge to slide all the way down. With that technique it could likely fit on other models well enough, but you could also design an adapter to customize the fit.