A remotely operated manhole cover for a tanker or trailer is provided. The manhole cover includes a hollow neck which is welded in place in the shell of the tanker or trailer. The neck defines an opening which allows access to the interior of the tanker or trailer for filling or cleaning of the tanker. A lid is pivotable about an axis between a closed position in which the manhole cover is closed, and an open position in which the lid is clear of the neck opening to allow access to the interior of the tanker. The lid is provided with an inflatable seal and locking flanges which extend from a rim of the lid. Pivotal locking members are provided on the neck and are movable between a locked position in which locking member engages the lid locking flange and an unlocked position in which the locking members are disengaged from the lid locking flange. Separate actuators are provide for the cover and the locking members. A controller is provided to energize the cover and locking member actuators and to inflate and deflate the seal. The controller activates the locking member and lid actuators and inflates or deflates the seal in sequence to unlock and open the lid or to close and lock the lid. The controller includes a manually operable switch assembly which activates the manhole cover to open and close the lid. The switch assembly is located remote from the manhole cover, and preferably near the bottom of the tanker.