I did the same thing on a band trip to FL my freshman year of highschool. There's still a high chance you could get caught as that smoke gets trapped in the bathroom with you till you open the door, but it worked for me. The fan helps a bit, but not much. Just bring along a sneak a toke and try to blow strait into the fan with small hits. While keeping the pipe covered with a towl while you exhale. Lock the door and have the shower on high. Maybe the steam/soap/shampoo smell will cover up the smoke. Also apply your deoderant and cologne before you exit the bathroom. Good luck soldier.