A sewage relief valve includes a cylindrical housing mounted on the upper end of an upper end of a riser connected to a sewer line, the housing includes a cylindrical through-bore with the upper end of the bore sealed by means of a dome cover held in place by a resilient O-ring, and a float supported beneath the housing on a lift linkage is responsive to rise with the level of liquid in the riser for forcing the cover from the end of the housing thereby relieving the sewage line. The lift linkage means is supported within the housing by support means which permits the linkage to be lifted and carried upward out of the housing by the float means when liquid flows therethrough.