Originally Posted by Campag4life

Don't use a lot of torque. Slippage is due to coef. of friction between mating surfaces. If you know the saddle height you like, mark the post with tape, lightly sand the Thomson post with 600# wet paper below the tape mark, wipe both inside of seat tube and post with alcohol and install. It shouldn't slip. Last resort? Hairspray...yes hairspray. Mark the post with tape again and spray the post with hairspray below the tape line, let dry for about 5 minutes and assemble. It won't slip. Thomson posts shouldn't slip because they are lightly serrated by how the post is machined by design intent.
HTH.