I recently had 2 buyers both perform a sewer line inspection, one in South Minneapolis and one in St. Louis Park. They both happen to use the same company, but both had completely different results.
Sewer lines can be constructed using very different methods. The most common ones are a solid pipe, usually PVC, and individual clay pipe sections, each being about 2-3 feet long. Each clay tile section fits into the prior section, and the joint between the tiles can become loose over time. When it becomes loose, tree and plant roots can start to grow in the joints, and these tree roots can get so thick, they will eventually clog the sewer line. This results in the dreaded sewer line backup where raw sewage is coming up from the basement floor drain or the house drains are draining slowly.
The sewer line inspection in St. Louis Park revealed that the sewer line had been recently re-lined and was in very good condition except for a tiny bit of roots at the very end of the line where it connects to the sewer main. This was very good news for the buyers as they wouldn't have to worry too much about the sewer line for quite a while.
The second inspection in South Minneapolis revealed a section of the pipe that was sagging. This section had come down so far, you could see the cracks in between the joints, and it was holding water (sewage). If you take a look at my crude drawing, you'll see what I mean. This is a sewer line that is showing signs of failure. It may still function correctly for now, but how long until one end gives way and the sewage has nowhere to go?
This is easily a $6,000-$8,000 problem. A sewer line company would have to dig up the yard, install new piping, and connect it to the city sewer line. This is not an easy task, and most people wouldn't even consider tackling it themselves. In the end, we backed out of this house due to the seller not wanting to lower the price of the house based on the condition of the sewer line. The funny thing is that a week later, the front yard was dug up and the seller was installing a new sewer line. When we found this out, we submitted another offer. It was accepted, and the buyers ended up with the home and a new sewer line. This $180 inspection saved the buyers $6000, plus we also lowered the purchase price by another $2000.
Furthermore, if the sewer line has a problem where it connects to the city sewer main, this is in the middle of the street, complicating repair efforts. The cost for repairs in the street would include digging up the street, and repairing the street. In this case, costs can be $12,000 and higher. I've seen some quotes in the $15,000 range.