There's a collar around the neck with that little downward facing square. Your arrow is facing the lock for the collar. I don't recall if there's a second lock opposite the arrow. Once the lock/s are free, the collar will slide up on the vertical ribs, and you'll be able to turn the neck out. The neck has rubber baffles that make it too easy to flood oil over the neck. FWIW I just cleaned mine up with compressed air and brakeclean. It did take a couple of times. I thought it was clean, but it kept weeping oil until cleaned a second time.