I was going to upload the .PDF of the pertinent section of the service manual, but it's 5 KB too big.
From the photo, it looks like the hose you are asking about goes to another "Y" connector. One side goes to a manifold vacuum port, and the other goes to the vacuum reservoir. If you were to PM me with your e-mail address, I should be able to send you the file.
Best of luck,
Scott