Abstract: The present invention pertains to a containment unit for use with a fill pipe of an underground storage tank. More specifically, the containment unit is constructed to collect any spilled fule in the filling process of the underground storage tank. The containment unit is provided with a floor having a coupling for connection to the fill pipe of the storage tank. The inner wall of the unit is of the bellows type to permit vertical expansion and retraction as required due to changing temperatures. Additionally, the floor of the containment unit is equipped with a removably inspection plug which permits ready access to the soil to take samples thereof thereby eliminating the need for disassembly of the containment unit to accomplish the testing.