Even if it is confirmed to be sciatic pain, there can be different causes for the pain. Not all sciatic pain is going to be helped the same way. That being said, there are a few stretches I have had success with when used regularly. Also, myofascial release works wonders. The stretches include having the client lie on the floor with bent knees, cross one leg over the other and pull the other leg in until they feel the stretch in the deep muscle of the glutes. This can be done sitting or standing also except you would have them slowly lower their upper body toward the thighs without rounding the back. Another stretch that is similar is lying on the floor with knees bent, grab one leg behind the knee with one hand and behind the ankle with the other. The client then pulls both the knee and ankle toward the opposite shoulder. Tight hip flexors could also contribute to back pain. Since we have a society full of people who sit at a desk all day it couldn’t hurt to keep the hip flexors stretched also. I personally like the stretch standing in a lunge position, keep the back leg mostly straight and lean forward until you feel the stretch in the front of the thigh. Hold 30 seconds then drop the knee down toward the floor a little, lean the hip slightly forward and feel the stretch higher up in the hip flexors. This stretch can be done with the back leg up on a bench/chair or on the floor with the back knee on the floor.
I suffered with sciatica pain for many years in my right glute. I learned a stretch that directly affected the impinged sciatic nerve and brought relief from the pain. Simply step forward with one leg, as if you are doing lunges, and hold. Stretch the trail leg (in my case, the right leg) without the knee touching the floor. I hope it brings you relief! – Michael