A manway gate assembly couples to a tank and provides a liquid tight seal. The manway gate assembly includes a gate selectively slideable in a first linear direction between an open position, a closed position, and/or an intermediate position between the open position and the closed position. The manway gate assembly includes one or more locking members arranged adjacent to the gate and moveable between a locked position and an un-locked position. When in the locked position, the one or more locking members apply a biasing force to the gate in a second linear direction perpendicular to the first linear direction to seal the gate to the tank and provide a liquid tight seal.