UDC stands for "Under Dispenser Containment" and is sometimes referred to as a sump, as it is a collection point for gasoline leaks or drips from the piping or in-dispenser components.

UDC's are installed flush with the tank pad or pump island, and the fuel dispenser is installed to the frame of the UDC and/or the tank pad itself. All fuel piping, vapor piping (Stage II vapor recovery) and electrical conduit is installed to the UDC using penetration boots or penetration fittings. Models with Single Wall construction are generally not continuously monitored but can feature mechanical float trip mechanisms to automatically shut off a double poppet shear valve, or an electronic liquid sensor can be installed at the lowest point. These products may be made of fiberglass, steel or a form of polyethylene or other plastic.

UDC models with double wall construction have an interstice that can be tested by either positive pressure or vacuum, and is continuously monitored by liquid paired with an electronic sensor to monitor the liquid level at the highest point, or vacuum monitoring. These products are typically only made of Fiberglass, due to the obvious advantages with no disadvantages. Unmatched corrosion resistance, fuel compatibility including various alcohol blends and overall strength. No elasticity, little to no flexibility and no deformations due to temperature changes.