What a general home inspection actually misses
A standard inspection checks visible plumbing — fixtures, visible pipe, water heater condition. It doesn't run a camera down the main sewer line, because that's a specialized inspection most general inspectors don't perform. That means root intrusion, bellied or sagging pipe sections, offset joints, and cracks in an aging clay or cast-iron line can all be sitting there completely undetected on a standard inspection report.
Why older homes specifically are the concern
Clay and cast-iron sewer pipe were both common in older construction and both degrade in ways that don't show symptoms until they're serious — clay from root intrusion working through joints over decades, cast iron from internal corrosion narrowing the pipe. A home can have zero drainage complaints from the current owner and still have a sewer line that's a few years from a real problem.
What a camera inspection actually shows you
A waterproof camera run through the main line shows the pipe's actual interior condition in real time — material, any cracks or offsets, root intrusion, and how much the diameter has narrowed from buildup or corrosion. It's the difference between guessing based on the home's age and actually seeing what you're buying.
When to get one during a purchase
Ideally during your inspection contingency period, before you're locked into the purchase, especially on any home older than 40-50 years or any home with a history of drainage issues mentioned by the seller. If a problem does show up, it becomes a real negotiating point instead of a surprise repair bill six months after closing.