Since this is the first result in Google, and there aren’t any real photos elsewhere, here is how to find it for others who end up searching like I did:

Climb on top of your cold engine, and shove/smash/reach your left hand behind the right side of the intake manifold. You’ll feel a metal tube with threads pointing rearwards:

 

I could have sworn I posted a pic of this before

 

But the last post on this thread was 12 years ago.

 

Every newer one I found wasn’t helpful. I’m trying to post my solutions to problems I’m solving for my car so that future users can see answers, since so many threads don’t have the solution posted. And again this thread was the top search result consistently.

 

it's truly in a terrible spot for diagnosing. Just glad there is one, pre 95 classics do not and have to cut fuel line to test pressure..