The current DWV layout in my tiny upstairs half-bath is a mess. There are leaking fittings, horizontal vents, and drain pipes sloped in the opposite direction! The "stack" for this bathroom comes up from the basement through a closet in the first floor. I plan to cut out the existing cast-iron stack and replace it with the one shown in the diagram below. I've already removed the existing toilet and sink, so re-installing and moving fixtures is not a problem. Would the layout in the following diagram be correct? The toilet drain passes behind the horizontal drain for the sink in this vertical view. The toilet and sink are very near one another.
I do have a problem with the venting, however. The "stack" is not contained in a wall and lies directly below a window in the bathroom above. Can I attach an air admittance valve at the vent location in the figure, or can I attach a single vent at the rear of the sink p-trap? How else might I get the vent to exit the building? Any advice would be greatly appreciated.
I do have a problem with the venting, however. The "stack" is not contained in a wall and lies directly below a window in the bathroom above. Can I attach an air admittance valve at the vent location in the figure, or can I attach a single vent at the rear of the sink p-trap? How else might I get the vent to exit the building? Any advice would be greatly appreciated.