Abstract: A corrosion resistant manhole unit having a rotationally molded plastic manifold forming a hollow chamber for providing access to sewer pipes to be connected to the manifold. A manifold inlet connector molded into the manifold for connecting the manifold to an upstream conduit and allowing an inflow of fluid to the hollow chamber. A manifold outlet connector molded into the manifold for connecting the manifold to a downstream conduit so that fluid flows out of the hollow chamber. A manifold riser molded atop the manifold having an open top forming an aperture for accessing the hollow chamber. The manifold riser extending upward from the manifold towards ground level for allowing equipment and personnel to access the hollow chamber through the aperture. A watertight removable riser cap is included for sealing the top of the riser to close and prevent fluid and debris from entering or leaving the manifold.