Dan,
Actually, I'm really not sure when I takes drinks from my water system...it just seems to happen at various times during the race. I think Manny hit the nail on the head. Wear your hydration system 100% of the time when you ride, and it will just become part of the norm. I even carry it with me while riding in sub zero temps. Somtimes, it seems as full at the end of a ride as it was at the beginning, but I never feel thirsty.
In a nut shell, drinking while riding has become so natural after having one strapped to my back for so long that it is just a natural part of riding. I am sure I must take my hand off to grab the hose, but never really know it's happening. A BIG part of this is running a stabalizer, as riding with one hand doesn't make me nervous.
One important point is the care of your hydration system (mold is a huge problem if you are not careful). I know folks that toss theirs in the freezer to keep from developing mold, but then they forget to toss it in to go riding. Here is what I do:
1. At the end of riding, open the fill cap on the hydration system and dump everything remaining onto the ground.
2. place your mouth into the hole so your checks get a good seal and start blowing.
3. While blowing, pinch the bite vavle until air comes out.
4. Repeat all of the above processes just to get any trapped water out of the bladder.
5. stuff the bite valve/tube into the bladder opening and hang to dry.
With this process of getting the water out of the sytem, I have been able to use the same system for almost three years without any mold. I have heard all of the fixes to mold, but the best fix is to empty the sytem completely of water so no mold can form.
Good Luck
Rick