that hasn't been my experience - my watering cups are attached to pvc pipe attached to a 275gal poly tote. Perhaps you are thinking of a different style of cup, or you have had very bad experiences.
Yes, but they can't clean their bills - that requires dunking. Which is why I first used the battery box, and then the short plastic 2 gal paint buckets.
I use cups, ducks can't use nipples, and I have some. They don't use cups well either, so I also have a dog bowl that fills automatically, a battery box with a float so it fills automatically, and a couple buckets I fill manually. They prefer the buckets....
8 Cups. One for each 4 or 5...