apartment building

I'm reactivating a 1980's era solar thermal system that's been out of service for about 15-20 years. It's all working now, but I have a concern. The potable water solar loop has two 100 gallon tanks. The tank hot goes via 1" pipe to meet the 2" cold feed to the 120 gallon commercial gas water...

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...