I own a 7 apartment multi-family building built in 1974. Sewer line is cast iron. We have clogs frequently and it appears cast is corroding. I know it's only a matter of time before I will need to replace it. Problem is, the building sits on a slab. It's also fully leased. Line runs left to right down the full length of the building, servicing each apartment one after the other until it exits the building under the right side wall. So, unless there's a new replacement method I'm not aware of, I'll be cutting up the slab inside each apartment to install a new PVC sewer line along with feeder lines to each drain (2 baths and a kitchen in each apartment). And then once new plumbing is installed and concrete poured I've got flooring to replace. So this is going to be a lengthy project. I can't envision how to get this done while tenants are living in the building. Any suggestions?