One common situation for commercial or multi-unit buildings still connected to the sanitary sewer system is to have a roof drain that runs down through the building and into the sanitary sewage lines.
There are two routes for disconnection in this case.
One is to redirect the rainwater onto grade. This method is appropriate if there is sufficient drainage at grade to handle the flow during rainfall.
The second route is to install plumbing that directs rainwater to a storm drain underneath the street.
Last updated Feb 6, 2019