When my nipples drip, it's always that they just need to be tightened a little bit. In my case, it's never the threading into the 5-gal bucket, but rather the threads that hold the upper and lower parts of the nipple itself together. You can unscrew it all the way and observe/lose in the dirt...
I'm using cheap nipples from ebay in a 5-gal bucket (with an auto-fill setup based on a stock tank float valve). The nipples work great! Regarding the person who said they're not using them yet because his chickens are in a brooder or are too small: I just recently saw a picture of a soda...