I never thought about sterilizing them... maybe that's why I've had two colds this fall/winter season. Ha!
I don't think the dishwasher would be safe as the high temperature of the water would probably warp the tip and definitely mess up the o-rings. I also saw on ECF that soaking them in alcohol is not the best method because it could dry out your o-rings and they could crack.
I would think dipping a Q-tip in alcohol and using it it clean the tip (avoiding the o-ring) and then rinsing them in hot tap water would suffice. But then again, you'd be taking advice from someone who has been sick twice in the past 4 months.