Section 331 (Speed Control): Reservoir-Vacuum: Description
WARNING: This page is about a different car, the 2005 Dodge Pickup and 2005 Dodge Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
The vacuum reservoir is a plastic storage tank connected to an engine vacuum source by vacuum lines. A vacuum reservoir is not used with diesel engines or the 5.7L gas powered engine.