Matt W.
WKR
Definitely helps explain. The trouble is that the Nalgene just barely fits, and takes both hands pretty much to get it in there, and then it's still a pretty floppy setup. A flexible water bottle seems like it would work way better, and basically eliminate what I think is a bad setup (for me).
Makes sense. It looks like pods8 has a better solution for a Nalgene bottle. Hopefully that will work better for you.