# Preparing an inert atmosphere reaction vessel with only an input?

One time, the graduate student that I work with was showing me how to prepare an inert atmosphere in a double necked round bottom flask. After drying it in the oven, she used a torch to drive out all the water vapor. Then she put septums over both openings, and inserted a needle connected to the nitrogen input through one of them, but with no outlet! I asked her to explain how any gas could escape in this set-up, and she tried but I was still very confused.

In a typical evacuation/backfill cycle, you can actually see the balloon getting slightly smaller when backfilling (assuming you have a larger flask than $25~\mathrm{ml}$. This is about as much as one looses to minute holes overnight. So it takes about 18 hours for the entire line to loose as much gas volume as a single flask has. No way that her reaction was water- and oxygen-free.