The vacuum reservoir over the passenger wheel we'll cover has 2 lines coming out of it. One goes to the intake. Where does the other line go from the reservoir? I'm struggling to make sense of the diagrams in reference to the reservoir in particular. Any help is a appreciated.

 

It goes in the direction of the firewall to the air blend box. Mine reaches rearward, lying on the RF wheel well and disappears under the fan body.
I looked inside and it appeared there was a splitter (a tee of sorts) in plain sight.
If you see the "impact/rollover fuel shutoff", the line will be in your field of vision.

It actuates a door which isolates the heater core from the AC air flow when "MAX" is selected.
Why it does this, I do not know.