jblackwood
Enlightened
Your mention of doing this when changing batteries is what mostly threw me, as the tail cap doesn't get removed just for a battery change. The only way that air could get trapped before reaching the o-ring would be if there was enough lubrication on the threads to make an airtight seal and my threads are dry.
If this method is actually working for you then I'm envious but I suspect that the best one I've seen posted so far has to do with heating up the light and letting the natural cooling cause a vacuum to draw the cap down. Every time I put the cap back on I hold the button down all the way as I screw it down and I suppose it's a little better than naught...
Air freely travels from the battery compartment to the electronic switch. I know this because when I change the battery, my normally flat button protrudes. I unscrew the tailcap (I have the newest model that can fit the new clip) and push the button in while I screw it back on and all is good!
I suspect this method works better than pushing the button down while changing the battery (at least for me) because less air is displaced when taking off the tailcap verses replacing the battery.