I want to put a bathroom in a large upstairs closet of a 1920's era home. Not sure of the dimensions but there is a cast iron vent pipe approximately 5" that runs through closet, out to roof & downstairs to sewer line (a straight shot through walls). It 90"s in the basement into the sewer line. Can I, or is it possible to install a toilet and use the vent pipe as a sewer line if it is vented above & below stool. We are selling the house and want to add another bathroom to make the home more appealing to a potential buyer. The home only has one bathroom at this time. I want to avoid having to tear the walls apart to put in a drain. Any other options that I could use? I'll admit I know absolutely nothing about plumbing & hope somebody can help. Thanks in advance.