Abstract: A plumbing system includes a tub having a drain fixture lodged within a floor drain opening. The drain fixture comprises a body member beneath the floor and a drain cap member inserted into an exposed open inlet of the body member. The body member has a passageway extending between the open inlet and a downstream open outlet in communication with a sewer. A pipe connected to the body member between the inlet and outlet has one end in communication with the passageway and another end in communication with an overflow opening in the tub above the drain opening to vent the passageway. The drain cap member moves between a first position allowing liquid to flow through the passageway and a second position preventing the flow of liquid through the passageway.