So we bought a gravity flow cup hog waterer (see pic below). The pigs drink from the cup but don't push the paddle in to get more water. So we go back and fill the cup, they drink from it but don't push the paddle to fill up the cup.
CJ has a good idea. I've also stood there and worked the thing for them when they are thirsty, showing them how it's done. Although I've used pig nipples on pipe and gravity fed from a 55 gallon barrel with good success. They need to be adjusted to get the right flow from the head pressure, but they do work consistently well. The important thing in either case is to teach them what to do to get the water. They are pretty quick studies.
"...specialization is for insects." - Lazarus Long