go around door ledges etc with a lighter and check how the airflow works in your room, eg. that the higher layer of air in your room is moving out while the bottom air of your room is flowing towards the hallway. It may change with weather changing, but once you got it figured out you can use the airflow properties of your building in your favor
Wow that sounds pretty stupid, reading now, but please don't think I'm crazy...
Didn't bother reading other responses so I'm sorry if this post has any redundancy to it.
I want to preface this by saying that I went to a university with a dorm "neighborhood" completely enclosed by a 12-foot gate, with one entrance/exit manned by security police 24/7 to check student IDs, temporarily confiscate dorm residents' visitors license (until they left the dorms), and to keep people on the no-trespassing list out. Campus police were about 15-deep, did routine (and random) patrols and had an agreement with the county's sherriff's office to do "drug-dog training exercises" in the dorms randomly four times a year (basically they would run dogs through the parking lot between every single car, the perimeter of the gate, and up and down all the buildings stairwells to let the dogs scan our apartments' front doors). Suffice to say, I've got experience smoking in a lock-down secondary educational environment.
The air purifier is a good idea. Scratch that, it was the best thing in my odor-eliminating arsenal when it came to tackling the smell of constant weed smoke between 4 heavy and habitual smokers in a single apartment. Keep the smoking as far away from the front door in your apartment as possible. If you're able, try and establish a house smoke room in the back that you can chill in. Seal the room up (windows closed, 2 towels covering the door crack for extra measure). Set up the air filter directly in the center of the room, and get a small fan similar to the one called Vornado (Google is your fried

) to keep an air circulation contained inside your room to better ensure all the smoke eventually filters through your air purifier.
There's another product you can order, an air freshener, that goes by several names: Blunt Power, Blunt Effects, BluntStyles etc. etc. Google that first name and it should take you to a website of the absolute best air freshener I've ever come across in my life (second best being Yankee Candle aerosol air fresheners). Anyways, 2 sprays from Blunt Power (which comes in literally hundreds of different scents-- my favorite is Baby Powder Vanilla)
while you're midway through a several blunt session in a super danked out room literally, and I shit you not when I say literally, completely eliminated the smell of blunt smoke
while it's still in the air. It's amazing and admittedly hard to believe by word-of-mouth online, but I assure you I'm not a salesman and this air freshener (marketed as a smoke eliminator, by the way) can't be described by any two words other than "the shit."
Also, Febreeze dryer sheets. Keep the dryer sheets on deck at all times, and try to snake a few in between your air vents so that your air conditioner or heat constantly blows out the lovely scent of freshly done laundry. They got hip to the dryer sheets at my school, though, and started writing people up for contraband when RAs would see them in the vents during room inspection. Easy way to avoid suspicion? Just take them down if you know you've got a health and safety inspection coming up.
OH!!!!! And with dormroom bathrooms, most have vents that allow you to remove bad smells from the bathroom. Most weed heads think this is a Godsend, when in actuality it can be a fucked up trap. The vents blow the air
somewhere obviously, and in some cases that happens to be right into the courtyard, or right below an RAs balcony, or some other very suspicious spot that school staff have learned to determine the smell's source from regarding bathroom vents. Not all schools are like that, but mine was and so were several others I've partied with friends at. Just be cautious is all I'm really saying... College and university is a pretty big deal and I completely understand not wanting to blow it over some stupid shit like an RA thinking he smells weed outside your front door.
If I think of anything else I'll come back to this thread, but I think that pretty much about covers it. I can't post links to sources of air purifiers or fresheners or anything, but if you have trouble finding some of the items I'm talking about then just PM me and I'll try to direct you to the exact products that kept me cuff-free after 4 years of feeling like I was going to college in a prison.