Some people recommend lancing and squeezing it out, but that is pretty invasive, and since I don't have experience with type of thing, I can only mention it. I would try Baytril from the vet, but I hope the increased Tylan helps. There was a case similar to yours last year that I can't find, and they treated it for weeks and weeks, plus tried removing the pus without success, and finally, it started getting smaller after a vet gave Baytril.