I wouldn’t automatically add it just because the building is older. If this is a multi-unit property and the relevant sewer is common property, an individual scope might reveal little that affects your personal repair liability. Ask management for any history of backups, root intrusion or line...
There isn’t a universal net yield that makes this worthwhile. I’d compare the unlevered net yield after recurring costs and realistic reserves with other properties you could buy at similar risk, then separately examine cash flow after debt. Before deciding, get the current tax history, a...