What the f%^$!! Is it possible for the vac. tree to blow fluid into the plenum????

[Stang_ROTY]

But how does gas or egine oil get into the upper manifold? The throttle body and intake was clean as a whistle when looking through the upper manifold with the cover off. Still new looking. I'm really trying to determine if my engine builder screwed something up becasue he attached the line to the vac. tree. What lines run in and out of the vac. tree on the firewall?