Abstract: The disclosed sump pump pit is modular, being formed from substantial planar lightweight top, bottom and side walls that when disassembled can be carried compactly stacked on one another to an intended sump hole, and can then be assembled and secured together as the rigid pit defining an enclosure sized to hold at least one sump pump (preferably two sump pumps side-by-side). Cooperating tongue and groove configurations on the side wall edges interlock these components in a tubular configuration, and the end edges of the side walls can be fitted into and secured in channels in the top and bottom walls, making the pit rigid. The pit walls are perforated for communicating the sump hole with the pit enclosure. Piping extended through the top wall allows water to be pumped from the sump hole via the pit pump(s).