I have the solution. Was smoking up with this dude one day and he told me he had smoked in the dorm for 6 months Heres how he did it:

First, the window has to be one of those push up/push down types, none of those wierd push out types.
Get 2 towel rolls prefer 12'
wrap them in towels at the edges and place it in the window. After messing around with it, it should be 2 rolls leading outside, insulated completely by the towel. Think of it as a intake / outake.

Theres a pic of it (see attachment)


All the area between the circles should be towels.

next scram fabric stuff in one of the rolls.

Now roll a J and inhale thru the clear roll (one without shit in it) and light and smoke. When u need to exhale, breth out thru the other roll while placing your j and hand over the first towel you inhaled from. This will block out the smell in the room and make you detection free.

And BTW: DONT BUY AIR HUMIDIFIERS OR PURIFIERS. They dont work and ppl have been banned in dorms becuase theyre such idiots. No refunds either

ENJOY!