Go underneath hood and look towards the bulk of vacuum lines on the drivers side firewall. You will see a couple of big yellow lines that connect to a check valve. One is for resevoir and the other is supply. Easyest way to do this is disconnect both , unlock doors with key from outside car, now pump one up until door locks try to move, that is supply. To ck the resevoir you will have to pump along time on the other one. Now if you have found supply and the door locks try to move but dont hold vacuum in lock or unlock its time to go to check points. On the drivers front seat pull up the carpet panel, on your left you will see a black cover, pull it up.
You will see red vacuum lines and green .Green are unlock and red are lock. Now connect the mityvac to one ( probably going to rear or drivers rear door) . Check these and see if they dont hold. You can watch the rear door and watch the lock try to move. Now if the vacuum lines going to the passenger side leak then do the same thing on the passengers side checkpoint. If all are ok and the passengers side going to the trunk still leaks then you can go inside the trunk and gain access at the gas flap actuator and check the trunk lock actuator and gas flap. Sorry so long , hope this helps.