It's not about the vacuum effect in the bottle, it's about how the nipple is constructed. When you suck on the end, the "neck" closes because of the pressure and won't let more milk flow. I'm a bit hazy on the mechanics because it's been a while, but I'm very sure of the end result.
I imagine you can easily try it and report back if you have quick access to a bottle, maybe you can shed more light on this.
I imagine you can easily try it and report back if you have quick access to a bottle, maybe you can shed more light on this.