I like a 2.0mm id because
@Dubminer recommended it way back in the doggy thread, and it
really improved my vape over my old std. 2.5, but whatever works for everyone is great.
On the True, I've accidentally left mine open a couple of times, for quite a while - 20-30 minutes, and even took a couple of hits. But still never a tiny drop of a leak since my very first build, a couple of months later. I don't think you need to worry about closing it at all while filling, if everything else is right.
And somehow, this tank produces far less condensate on top of the mod than anything I've owned, including the doggy. I couldn't be happier with this tank.