Wheres the best place to tap a boost gauge into without drilling into the manifold...

So far we've tapped it off the fuel pressure regualtor line...Or in mean the tube off the manifold going towards the front of the car, black rubber line to a small canister.

Brake booster line? or does it have some sort of valve in it to stop boost? Because doesn't a normal brake booster work off of vacume?
Hrmm <scratches head>