A manual, in-door lock arrangement is provided for invalid bathing units and the like, of the type comprising a bathtub having a lateral opening in one side thereof for ingress and egress, and a door slidably mounted on a hinge-less track assembly for vertically translating the door between open and closed positions to selectively open and close the bathtub opening. A compression seal is disposed between the mating edges of the door and bathtub opening to form a watertight seal therebetween. The lock arrangement comprises a hand-operated actuator arm pivotally mounted on the exterior side of the door, and an elongate rod pivotally mounted within the door with latch arms attached to opposite ends of the rod. Latch plates are mounted on the track assembly at a location adjacent the latch arms when the door is in the closed position. A link mechanism interconnects the actuator arm and the bar, whereby downward pivotal motion of the actuator arm rotates the latch arms into engagement with the latch plates, and positively pulls the door down into the closed position. An over-centered latch mechanism securely locks the door in the closed position.