For about $30 you can purchase a hand held vacuum pump with a guage to test most lines. It comes with different fittings for most size hoses and goes to about 25" of vac.
which is more than enough. You can watch the guage for how quick the bleed off is and since the motor isn't running you can hear it bleed...if it does. Most NAPA, Autozones and PepBoys carry this.
Bad news again, if you need to get to the valve/potentiometer assembly at the top of the dash. If the car is old/high mileage think about just cutting a flap over the center area to work in that section. When finished just put a Coverlay dash top in place. If you need to gain access again, it's real easy to remove cover and replace.
This way you don't have to pay/do remove the whole dash and possibly screw something else up doing it!