Piriformis syndrome is a pretty common dysfunction pattern that usually presents more in women then in men. Described literally as a pain in the butt. It can present not only with local pain, but also a sciatic type pain as the sciatic nerve can become compressed over time when the Piriformis is tight.
Soft tissue methods directly on the Piriformis can lead to short term improvement. The question becomes why is the Piriformis irritated or feels the need to tighten. This is how long term improvement is achieved.
One possible answer lies in the surrounding anatomy. Looking at where the piriformis has attachments, the lateral portion of the sacrotuberous ligament has fibrous reinforcement from it. The sacrotuberous ligament is made up of three separate bands, medial, superior and lateral.
The sacrotuberous ligaments role is to limit nutation of the sacrum. Further down the line, the biceps femoris muscle (lateral hamstring) has direct attachments to the sacrotuberous ligament. The biceps femoris now is understood to contract before heel strike. Without a strong biceps femoris, gait mechanics will be changed and Sacrum/Iliac (SI) joint dysfunction can occur. This may lead the piriformis to tighten up to try to help stabilize the SI joint.
While one can never achieve great results with just following a cookie cutter recipe in manual therapy, recognizing patterns is always helpful. Test for weakness in the biceps femoris next time piriformis pain presents in your patient/athlete. For the athlete dealing with this roll out the hip rotator complex and perform some hip/hamstring Swiss ball leg curls with the feet slightly turned in to try to target the biceps a little more. Try this everyday for two weeks and see if the pain in the butt leaves.