As long as you're not breathing through your mouth to avoid smelling something, constant exposure will dull the senses to it in about 2 minutes, if not less. So, by the time that everything's sorted out, no one should be really smelling it if they aren't intentionally trying to.<br/><br/>It's like entering a locker room at a gym or a hospital hallway, the smell of sweat in the lockerroom becomes less noticeable, as does the scent of disinfectant in a hospital. I can't see any reason, besides wanting to smell the stench, that anyone should be effected by it  any more than an inconvenience by the time that they enter the pipe..<br/><br/>Moving at 10' a round, 10 rounds in a minute, you should be able to travel nearly half of a mile in 24 minutes; I can't see the tunnel being that long since they seemed to literally leave one room and enter the next. You may be wasting the spell for 40 or 50 feet of movement.