there is one technique we use in our set up, position the patient in side lying with affected side up, keep his lower leg straight and rotate his trunk away from away from you till you find the final degrees of rotatory movement at his lumbo sacral joint, then flex his hip and knee to 90 degrees and holding the gluteal region of the patient with your cupped hands in a forward bent lunged position, turn the patient a little towards you, you can either give a sudden thrust or gentle grade 1 or grade 2 mobilization by thrusting the leg posteriorly using your hip(that is where his knee joint would rest), i hope this is clear, if not refer any manipulation book, this is commonly used technique, and other wise as far as assessment goes you can try stokes test, and lots lmore are there