Sounds like a building I once worked in.
It was 25 years old, when the toilets at one end of the building began backing up. It turned out that a sewer main tile in the bldg. was installed backwards, so after 25 years of sludge building up on the backwards joint the pipe clogged.
Contractors had to excavate down the middle of the hallway, 6 feet deep, to replace the tiles.
Major time lost on a 200 million dollar contract. The building was leased, so the owner took it in the shorts.
There were at least five stores in various parts of the country closed for 6 months at the same time for plumbing problems. The employees were not given any prior notice.