Are they dripping all the time or just when a chicken is using it? If the former, you might want to try some teflon pipe thread tape on the nipple threads, or another layer of it if you already did that in the first place. If the latter, try raising or lowering the bucket...if you find the right height it makes it easier for the birds to drink without dripping as much. I've heard from some folks that they got super cheap knock-off-brand nipples that dripped no matter what they did. I haven't had that problem.
