Depends on your dorm, I got Bacardi when i was on res but i shared a washroom with my roommate (it was in our room, along with a kitchen + our two bedrooms). I had him in a 2gal with no filter just because in my res i wasent ALLOWED pets, but i sneaked him in! lol Goodluck :)
I've been out of college for a while now, but when I lived in the dorms we only had 1 community bathroom per wing (~25-30 people).
A girl 2 rooms down from me had a betta in a ~2-5gal or so, and I remember her hauling it down to the sink regularly to change the water. Pets weren't allowed, so we'd let her know when the coast was clear to do so.
At my residence hall we're only allowed a maximum of a 10g tank and only fish are allowed. For my summer semester of 6 weeks water changes were a bit of a hassle. What I did at the time was scooped my betta into his store cup, emptied out some of the tank water via small bowls, carried the now-light tank to the kitchen, dumped the water leaving the gravel in the tank, swished the gravel getting the crap out, refilled it with water half way, carried back to room, refilled with bowls, dechlorinated, put the heater back in, floated fish, and then let him out, and passed out. lol
And right now, I am cycling my 2.5g tank, see my thread. :p Fish is currently in another 2.5g tank. I just dump that water into a 5gal bucket now, and dump it out in the shower (I clean the shower afterward) because we are in a suite of 8 girls per 2 toilets, 2 showers, 2 sinks. Swish the gravel and stuff around in the bucket, dump that, refill bucket, dump back in tank, heat water, float fish, fish back in tank. MUCH easier! Although once I cycle, 25% siphons once a week only >_>
This'll be my second year bringing Geist to the college dorms. He's not crazy about the 4-hour car ride and it takes him a day or so to get used to being in a different place, but so far he's done well. My roommate and I have a room with a small bathroom attached to it, so it's very convenient when I have to do water changes. I keep the tank up on the desk right by the bathroom door. =)
I do worry about my roomie using hair sprays and such though. I know she only seems to do it in the bathroom or on the opposite side of the room, but I dunno how far those particles can float in the air. Wouldn't want my fish water to get poisoned. =<