Never Never Never sign a lease or buy a building without a sewer inspection.

I can't tell you how many customers I have that are just sick. They hold leases on their restaurants or buildings and they come to find out that they have major sewer or drain line problems that have clearly been there prior to their move in. Unfortunately most commercial leases that I am aware of make the tenant responsible for all the drains and sewer lines within the building up to the mainline tie in outside of the building. I have a sweet lady, we'll call her Edith. She has been in this restaurant space for 6 or 7 years and she has constantly had to fight various drain problems. We have smoke tested her place several times on different occassions because of very strong sewer gas leaks within the building. We found degraded vent pipes in the walls and in the drop ceiling. These sections of degraded pipe allowed sewer gas to enter the building and it was affecting her business in a big way. We find and fix her problems when they pop up but there is a cost. The cost of the test, sometimes the walls have to be opened then repaired and then there is the business lost. That's just the vent pipes.
She also has regular sewer line backup issues because of degraded cast iron lines. Some lines are old and very rough. Sometimes this can be helped a bit with hydro jetting. Hydro Jetting with a large powerful machine can smooth out this rough pipe to some extent but if the pipe is getting thin with age or worse yet has holes in it, there isn't alot you can do short of major repair. The repair costs for what Edith is facing are easily in the ballpark of $6,000 plus. All this falls on her because of the way the lease is written. Take a look at the following link that shows a video of a seriously cracked sewer pipe that runs just under the corner of an apartment building.
http://www.superjetdrains.com/videos.php
We were able to line it with a cured in place pipe liner. If we had to excavate things would have been very expensive.
I would strongly recommend to anyone who is considering buying any sort of a building or leasing a property that they perform a camera inspection of the sewer and accessible drain lines. I would suggest a sewer and drain expert or specialist as opposed to just a run of the mill plumber. The specialist is going to have a much better understanding of what there looking at because it's all they do. If your in Southern California, give us a call. SuperJet Sewer and Drain Cleaing. SuperJetDrains.com It is what we do.
A visual inspection will quickly locate problems like a severe belly or low spot in a line that acts as a collection spot for debris. These are very often the cause of repeated backups. These cant be fixed short of digging it up and repairing it. ( We just did a diagnosis inspection of a beautiful house worth over a million dollars with a wide open floor plan and a long span across the house covered in beautiful stonework. The sewer line runs across the house under this same stonework and is plauged with multiple low spots or bellies in the line that regularly cause backups. The only way to fix this is to dig it up and regrade the pipe run. His only other option is to hire us on a regular basis to do a preventative maintenance with Hydro Jetting the sewer line.)
The other thing that comes to mind is that now many cities are making the homeowner responsible for the entire sewer lateral that runs from their house all the way to the cites mainline tie in point in the street. This is serious stuff. If you have a problem in that run after it hits the street, the cost to repair can be huge. A common number for a repair in the street with all it's additional issues, permits, certifications and costs can go $30,000+ very quickly. Think about that for a minute. How many houses or properties have you bought and did you ever do a sewer inspection?
One last thought, I do this for a living. About 50% of the time when we run a camera to inspect a line for whatever reason, we find a problem.