A mechanical closure device comprises an enclosure having four sides, a top and bottom and defining a discharge opening at the bottom. A floodgate assembly is interiorly removably mounted to the enclosure and comprises a pair of doors pivoted on a hinge assembly between an opened position and closed position. In the closed position, the doors seal against the flange to prevent passage of water through the discharge opening. A discharge drain assembly is preferably disposed on one door and has an opened and a closed position. An appendage is provided to facilitate opening and of the door. Upon removal, the floodgate assembly is stably positionable on a multipositionable service rack. A multipurpose tool is employed unlatching the floodgate doors and slidably removing the floodgate assembly.