I'm sure you could modify it for that purpose however, how far are the rooms from the fog machine itself? My thought is that is it is not centrally located you may get a ton of fog in one room, some in the second, and a trickle in the thrid.
Like Haunted said.. depending on your foggers power, you may not see much fog by the 3rd room with the other passages for it to travel as well. I would at most use it for 2 rooms. Use a Y adapter and try it out, the fog should split up evenly between both sides. How far are you placing the fog machine from the rooms... how long is the pvc, and how powerful is your fogger.