1998 Chevy S10 Vacuum lines

I replaced two vacuum lines, one of them (a 5/32" line) featured in
this video near the brake master cylinder (outside of it towards the
RH inner fender) and it controls the blower air duct directions:

https://www.youtube.com/watch?v=hdv8J1xb4Ck

and the other one was a 7/32" line running from the top center above
the engine as the vacuum source to where three meet at a tee fitting.

My question is, where does the 3rd one (also a small line, probably
5/32") go to? While pulling the old 5/32" line off the fitting, I
pulled the 3rd one out of wherever it was routed to. I looked under
the box ahead of the place where the 3 lines meet at the tee and
couldn't see anything, but that's the direction it looks like it was
pointing toward.

I plugged it for now and have no issues with the ducts working
properly, but I don't want to leave the other line disconnected very
long. Is there a vacuum hose routing diagram anyone might be able to
point me to that might be helpful?

One other related item was that there was a small plastic thing
between the tee and the 5/32" line that apparently feeds the blower
duct positioner. I removed it when I did a quick fix a few days ago
and now don't see any need for it, nor do I remember which direction
it was inserted in the line. Any thoughts?