When purchasing an apartment building, most investors I represent, will get a Sewer Inspection and for good reason. A sewer inspection, is where a company comes to the property and physically places a camera at the end of a wire, inspecting and recording the main sewer lines. You can watch as the camera maneuvers its way down the sewer line or they will give you a copy of the recording and an explanation of what they found.
At a 35 unit property in Riverside where I was representing the sellers, the camera located a collapsed sewer line under one of the units. The buyers canceled escrow. The sellers decided to fix it, by breaking the cement floor of one apartment unit and then sold the property with a clean bill of health.
Another four unit property in Cypress Park where I represented the buyer, the camera located a break where the sewer line connected to the main City line. The sellers credited my buyer $12,000 to fix it after escrow closed.
When I represent buyers, I always suggest they get a sewer inspection and the reasons for getting one.