You must sanitize ANYTHING that your beer will touch. Siphon, tubing, keg, probably should even spray down the neck of your carboy after you take the airlock and stopper out. Remember, you can't over sanitize but you can definitely under sanitize. I usually sanitize everything. Even my clamp that goes in the outside of my tubing. Not because it needs it but because its easier just to throw everything in the StarSan at the beginning and not worry about it later.