IME the nipple drinkers are a great solution IF you can get the birds to use them.
If it were me, I'd order a few nipple drinkers from Ebay (they're dirt cheap shipped from China etc), and screw them into the bottom of a 5 litre bucket, just to see if your birds will use them. If they will, you're sorted because they never need any cleaning at all. Just beware that if you try to screw them into a round pipe, they may not seal properly.

If they won't use those, the hanging auto-drinkers are also easy enough, and can be cleaned by wiping round with a rag. They're harder to rig up, and more expensive though.

The best way to rig them up will depend on the layout of your pens, but one good way would be to have an elevated water butt in the middle of the area (filling off a ball-cock), and then daisy chain the drinkers off that until all the pens are sorted.
HTH!