Abstract: A stackable elastomer adjustment ring is provided for the construction of the adjustment courses or manhole chimney portion of a sewer system. The adjustment ring is circular and includes concentric grooves in the upper and lower surfaces. Sealing rings are provided corresponding with the concentric grooves and are positioned between the adjustment rings in the grooves when the rings are stacked one on another. The adjustment rings are stacked one on another with respective sealing rings between them to provide a manhole construction which is resistant to infiltration, chemicals and freeze-thaw cycle damage.