Abstract: The present invention provides a collection tank for use under the floor slab of a building or slab on grade for collecting ground water from the surrounding soil and from weeping tiles. The collection tank comprises a collection tank having an upper tank portion and a lower tank portion, a plurality of perforations in the upper tank portion of the containment tank portion for receiving ground water, a plurality of cut-out ports in the outer wall of the upper tank portion of the collection tank each for receiving an end of a respective weeping tile line, an overflow port for communicating excess water to an overflow line, and a pump for pumping water in the collection tank to a location external of the collection tank. The collection tank also includes one or more collection tank extensions which can be added to the top of the collection tank to ensure that the weeping tile lines, when connected, are positioned at the proper angle to ensure efficient water flow into the collection tank.