So, I made several drinkers for my pens with the chicken water nipples...I took bottles laying around and installed the nipple in the cap, if it was a bigger bottle or jug, I put two... Well I noticed it was not flowing out of the pins when pushed like they should be... If I pressed on the side of the bottle, even a little bit, a nice stream of water came out when pushed... One of my bigger jugs, has two nipples on the bottom of the jug and the cap on top. well, I couldnt get the water to come out right, then I decided to try something and I opened the top slightly so air could go in, and WALA, a nice stream came out..
The only ones that seemed to take interest to them was the Chocolates, but after no water came out, they ignored it, I havent been out yet since I fixed the issue.
But I had found 40 nipples for 10 bucks on ebay.. sweet deal
You found the answer they have to have an air hole at the top of the bottle when hanging, if not you will eventually form a vac cum and no water will come out.