if it is "leaking pus" I'd be pretty tempted to open it a bit more and clean it out. If youdo, keep everything clean as possible, clip or shave the hair out of the way - open to the bottom of it so it can drain - squirt some peroxide in to foam it all out. Clean it good and keep it open so it heals from the deepest part out and doesn't close up on something and start all over. If it is hot or calf is running a fever some antibiotics are warranted as well.