We recently had a small sewage backup in our basement (2nd time in 7 yrs) which got resolved after rodding out the line. The plumber said this issue was caused by corrosion in the iron pipes catching material as it heads to the sewer, and suggested shooting an epoxy liner through to smooth and reinforce the piping (w/50yr warranty), but would need to install an external cleanout first to avoid trashing our finished basement during the liner installation process (we only have an internal cleanout). With the high cost to have to the work done (~ $4k for lining, $3.5k for external cleanout due to having to dig 10ft down to access pipe), I'm trying to think through our options. If I do all the work now, I have the peace of mind of not having to worry about future issues and I can have the digging where I want it. If I don't have the work done and the pipe breaks, the digging is dictated by where the break is and the potential mess from any backup. We are planning some landscaping, so I would want any digging done prior to this, so maybe I could just do the external cleanout now and hold off on the lining.

So this has raised a few questions:
1) On average, how long do iron sewer pipes usually last (ours is about 35 yrs old)? During the videoscoping, nothing looked out of the ordinary - just some rust - so how long could I reasonably expect the current pipe to last?
2) Are there any advantages to having an external cleanout, aside from the ability to install this liner?

Thanks for your help.

Before I'd spend $7,500, I'd have the line augered out every couple of years. For the most part, this is something that a DIY'er can do for the price of the tool rental. Spending $3500 for a cleanout does nothing but allow the plumber to work outside, makes him a good profit but won't stop backups.

Thanks for the feedback. I just spoke with a person in our Public Works department for the city and his responses were similar to yours. I did determine that the cast iron only runs through the house, and then connects to clay once outside the foundation. We've don't have any issues with tree roots, so everything looks good there.

Clay is more logical. The problem with clay is that the pipe is in sections and roots find their way through the joints. I would do a pre-active cleaning every 2-3 years. Put the $7500 into foreclosed houses!!