I had one on my shoulder that was about the size of baseball, for years, and my doctor said it would be painful to remove..so I left it there...until finally smell pushed me to the point of trying to drain it. I had the same experience where I poked it with pin, and got a stream fly out. It relieved the pressure temporarily, but it built up again. So the next time I used an exacto knife and made a slice across the middle. One firm squeeze and everything came flying out. I've been treating it daily by first dipping a Q-tip in Clorox and wiping the entire interior surface of the empty sac. Then I do the same thing with some Betadine, and pack it with gauze saturated with Betadine. I've noticed the interior of the sac was initially coated with white cells (probably the keratine cells), but now the white cells are gone and the interior surface looks smooth and pink. The interior seems to be shinking, so I'm hoping this going to continue to shrink. I also just started an additional treatment of a thin layer of Bentonite clay to the packing to help draw out the remaining keratin cells and dry it out.