Help ID three-way vaccum port

[1989accordaz]

The location of this 3 way joint is on the driver's side, 89 accord, Carb,automatic. One line goes to the idle boost throttle controller...where does the empty port goes to?

Pretty easy to see, once you open your hood, is right by the break master cylinder and the carburetor.

I look at the Vacuum connections on the service manual and I just can't see this three way joint.

Thanks in advance.