Power drum brakes questions??

To check for a vacuum leak in the booster put a vacuum gauge on the intake manifold. Take a reading and write it down. Now remove the vacuum line (large one) going to the booster from the manifold, cap it off and take a new reading. Should be the same reading as the first one. If off by more than a inch or so you may have a leaking booster. While you are at it check the vacuum check valve on the booster-you can blow through it one way and not the other. The check valve is the black plastic part that the vacuum line plug on to at the booster. It pulls off the booster but takes a strong pull.