When I did it, my exhaust wasn't hooked up. Just kept slowly turning the crank until I heard/ felt no more air through the dp elbow.
Maybe put a psi gauge on one of the vac lines coming from the intake to see if your maintaining pressure? That's what I did anyway to check the intake before I went on to check the ic piping. Just make SURE you have your air regulated!
First, I had some 1/8" piping laying around I used with a ball valve to make a sort of wand with a shut-off on it. I set my regulator to 5psi, charged the intake to 5 psi as read on the psi gauge, then closed the valve and watched the gauge to see if there was a leak.
That's just what I did....there maybe a better/easier way to do this.