Tandem (dual ) brake booster, how to detect leaking diaphragm ?

[johannes]

If I suspect a small vacuum leak in my tandem booster.... how do I test this ?
At the moment the booster is out of the car.... so I'm thinking ;
Connect the booster to the idling engine via vacuum hose...and listen ?
...any further test that can pinpoint whether I have a small leak or not ?

[roadman5312]

    Well testing in the car, press firmly on the pedal, engine off. Start engine, if pedal sinks some, booster working. Might be able to duplicate this process off the car.     Anybody else  ??