The smaller hose on the flame trap tends to deteriorate, as you discovered. It should connect to the vacuum stack manifold, second nipple from the top. The other poster Dennis has the right link:

http://volvospeed.com/Repair/vacuum_lines.htm

Look at the second picture down from the top. The small black plastic manifold in the middle of the pic is just behind the idle air valve. There are two small hoses connected to it going toward the rear of the car. The lower of the two hoses should connect to the small port on the flame trap. I've just been through this too. Hope this helps.

Gerald C