The Importance of Scoping the Sewer Line
One of the most common missed pieces of due diligence is to scope the sewer line. It only took me a couple of broken sewer lines where we had to dig out the entire line before it became clear to me that this was something that we should be doing.
A lot of properties, especially those built between 1940 and 1980, have sewer lines that were made out of a clay composite that has proven to wear down rather quickly (or Orangeburg which is even worse). On newer construction, this step can usually be skipped and while I would still recommend scoping the line on older properties, generally there is a better chance that those lines are OK because they are more likely to be cast iron or to have been replaced already.
A sewer inspection can cost over $200 if done by Roto Rooter or Snake and Rooter or the like but I've found several plumbers who will scope a line for $100. And given the average cost to replace a line is $3500 to $6000, it's well worth it. Especially since you can use this to negotiate with the seller and get a reduced price. The plumber can also tell you if the line needs to be snaked out which is relatively cheap and much better than the alternative of waiting for the tenants to call and yell at you for a sewer backup.
However, there is a risk that the plumber will convince you that the line is completely shot and needs to be replaced when it simply needs to be snaked out. So make sure to go with them when the video the line. A few roots here and there shouldn't be a problem. Just snake it out and remember to flush root killer down the drain every so often. It's offsets and large bellies or major root intrusions that should be the primary concern. Indeed, it's probably a good idea to tell the plumber that you already know the company you will use to replace the line just to prevent there being a conflict of interest.
Still, while it's important to be cognizant that the plumber may try to oversell the condition of the line, it's absolutely critical to know what condition that line is in.