Internal mobilization of the joint is usually the last recourse. It can be very effective, but neither the patient nor the practitioner looks forward to it and I think there are much more comfortable and still effective ways to accomplish the same desired results.
I have actually had much more success with external mobilization utilizing either direct mobilization at the inferior pole of the coccyx, or a sustained mobilization combined with patient movement.
I also find that many of these patients have a concurrent sacroilliac joint dysfunction (because they hurt themselves initially with a fall or other mechanism that affects the surrounding joints) that is often not addressed simply because most practitioners do not know how.
Unfortunately, many of these patients get passed from specialist to specialist without any real lasting relief. And yet within a few visits of directly addressing the biomechnical changes needed in the joint, it seems like magic occurs with relief of pain. I was referred a patient just two weeks ago that went to an orthopedic surgeon begging for relief from 20 years of "butt pain" and asked him to do whatever surgery necessary to help her problem. He sent her to me to just calm down her symptoms sufficiently that he could actually assess the problem prior to surgery. In two visits with manual therapy she was pain free from over 20 years of excruciating back pain and was discharged from mine and the surgeon's care.
This story has played out for me several times over the years.