A gasket for a railroad car manway nozzle and cover includes an inner leg portion and an outer leg portion joined by a generally planar annular body portion defining an upper annular cover sealing surface and a lower annular nozzle body sealing surface. Concentric annular chevrons are formed on the upper and lower annular sealing surfaces. In one form, the chevrons have a uniform height relative to the upper and lower sealing surfaces. In a modified form, the height of the chevrons varies relative to the surfaces from which they extend. The height of the chevrons is a minimum where the gasket is radially aligned with cover clamping bolts and a maximum at radial locations midway between clamping bolts. A tab depending from the outer leg portion provides visual verification of the presence of the gasket.