First let me say the company you hire is very important. We ONLY recommend hiring independent sewer inspectors. At $5000 to $25,000 for a major sewer repair, an inspection is important peace of mind. The sewer is one of the most expensive parts of the home we can’t see.
So When should a buyer have a sewer checked out?
I tell clients buying an older home it is absolutely a good idea to have it checked out. In Seattle of course, nearly all new construction is on a lot where there was once an old home. All too often, the sewer line from the old house is tied into without completely replacing the line to the street. As a former contractor, I can see the cost benefit ofsaving as much of the old sewer as possible.
This shared sewer between an old Seattle home and a brand new one. Having a sewer problem is bad enough, but having to work with neighbors too can make it more complicated.
Not all companies will pull a toilet, and this is sometimes the only way to get a good look at the sewer. We were on an inspection and the scoping company would not pull a toilet, and could not get his camera all the way to the street sewer. The customer paid $250 for marginal service and still has no idea if the sewer is okay.
Some things to be looking for that may mean sewer trouble:
1) Sewer snakes, root growth inhibitors, and excessive drain cleaners.
2) If there is a sewer clean-out and the cap is different from the rest of the plumbing, (a rubber expansion plug in a cast iron drain for example) instead of the original brass cap, there had likely been work done on the sewer lines.
3) Look for stains at the floor drains in basements, foul odors, and tags from a sewer cleaning companies.
4) Sinkholes in the yard and movement of the soils, especially for steeply sloped lots.
We got a note from a client after they had a sewer check after we recommended it. This home was 100 years old and they had 4 bottles of drain cleaners in the basement. He said, “We used (a recommended vendor) per your recommendation (and suspicion during the inspection). It revealed a ~$1,500+ issue that could have turned worse down the road, so it was money well spent.”