Yep..so.,. I got one of those nipple thing waterer.. none of my birds know or learned how to use it.
Might have to train them to use it. Take away all other water sources and then when they start looking around for water "peck" at the nipple with your fingers and let them come over and investigate it OR pick up a couple of the higher ranked birds and use their beaks to press the toggle until water comes out, let them drink, repeat. I don't consider training done until I've seen every bird drinking from the nipple, and if you have birds that are a little derpy or something like a crossbeak, it may take them longer than the others to pick it up (can take weeks in some cases).
You still have some time to train them to use it, though depending on the type of nipple and your temperatures, the toggles can possibly freeze, so it may not be a good idea to rely on a waterer like that while you're gone.