Using a foam roller

Foam rollers are an excellent way to target muscles that may be difficult to stretch or self-treat, such as piriformis. This video explains how you could use one to good effect.

You can buy foam rollers from Amazon:

White Foam Pilates Roller - 90cm x 15cm (6") diam - £17.90
Foam Roller White 90cm / 10cm (4") diam - £15.80
Foam Roller White 10cm - £18.31