The vacuum nipple on the heater/water valve is connected to the larger vacuum nipple on the back of the heater controls. Another hose that tees off of a hose coming from vacuum switch connects to the smaller nipple on the back of the control. The main vacuum feed is part of the vacuum harness and goes through the firewall on the passenger side near the floor, across the fire wall and up to the vacuum canister. Another vacuum line goes from the vacuum canister to the vacuum source on the intake. On my Charger, the "professional" shop I paid to work on it while I was overseas completely messed up the vacuum hose routing and left me with massive vacuum leaks and the heater control valve with a hose attached to it that didn't attach to anything else. It took a long time to sort it out.