A concrete washout container with leakproof sealing lid. The device has a lid portion with a base and lip structures extending around the base, each lip structure having a first contour, which first contour extends from an upper end of a generally vertical lid portion wall, which generally vertical lid portion wall extends from the base, wherein the lip structures are flexible along the generally vertical lid portion wall. The device also includes a bin portion, the bin portion having an open mouth, the mouth defined by a rim structure located around a perimeter of the open mouth, the rim structure having a second contour which second contour extends above a top end of a generally vertical bin portion wall section, which generally vertical bin portion wall section connects at a bottom end to a generally horizontal bin portion wall section, and which generally horizontal bin portion wall section connects to sides walls of the bin portion, which side walls extend upwardly from a bottom of the bin portion. The first contour, the generally vertical lid portion wall, and an outer perimeter of the base of the lid portion are complementary to and detachably and sealably contact and engage with the second contour, the generally vertical bin portion wall section, and the generally horizontal bin portion wall section of the bin portion.