I've never had a problem getting birds to drink from it. In fact, I have just bought two beautiful pullets and upon arrival, put them into their quarantine pen which had a pitcher with a nipple in it. I showed it to them by pushing on it with my finger and they looked at me like I was nuts! But once I kept pushing on it enough that a stream of water was coming out (chickens love running water!), they took to it immediately. The nipple waterer needs to be the only water source from the moment you put it in the pen, do not leave any other source of water in there- otherwise they'll never drink from the nipple. Good luck, I love the nipples because they're so much cleaner!!
I also have the stainless steel nipples, I got mine from farmtek. If you check out my byc page, you can see them!