In my opinion you would see very little or no changes by adding seafoam to your car. It can aid in cleaning carbon deposits from valves and combustion chambers but my experience with it is that it has very little effect. I can't imagine it would help you pass an emissions test.
If you feel you must add it to a vacuum line, check under the hood of the car for a vacuum diagram. Start the car and pull a small line off. Clamp it with some pliers or something. Stick the end of the hose into your Seafoam and slowly release your clamp allowing seafoam into the induction system. The engine will sound rough and it will smoke like a big dog for a bit. Rev it to work it through. Repeat this until your 1/3 bottle is gone.