If it has galvanized metal pipes, those eventually decay and start to flake, which causes blockage.

Additionally, some contractors will also install an ejector pump to pump waste from the property over and above the check valves back into the sewer line as once the check valve is activated, the waste from the property is unable to leave and go into the main sewer line until the blockage is resolved.Although, I can't personally recommend one specific contractor, I've read good things about The Real Seal, although they may only work on another drainage options (i.e. drain tile). 

If it’s on a slab, duct scopes can reveal blockage, disconnects, decay, and is a great idea.Scoping a sewer line is a great idea if there are a lot of trees on the property, people drive or park where the line runs, or the house is very old.

A blockage in the city sewer main flooded our dupex's lower unit with two feet of sewage.

He found that the cast iron under the basement has some corrosion and would probably need to be replaced as another blockage would probably happen.

The head pressure of the water will usually push through whatever blockage is in the trap arm between the sink and vertical stack.

The blockage is so severe that this is going to be a several thousand dollar repair.

Mine has a clause that reads: "Tenant shall be charged for repair of drain blockages or stoppages, unless caused by defective plumbing parts or tree roots invading sewer lines."

Have the licensed plumber that was initially called for this issue provide you with a report of the items found as the cause of the blockage and the recommendations, preferably you should also have photos of the items causing the blockage.

They will have to open this area to remove/push the blockage here to get proper flow.