The pupil set him to watering a flower, but Beezlebub went on watering it until the room was filling with water. At that point, the man, having remembered he left his book unlocked, returned and dispelled Beezlebub.
A student gave the man a task to water a flower, but Beezlebub went overboard with the watering, flooding the room. The man then remembered he'd left his book unlocked and dispelled the entity.