What is a sewer line?

Start at the cleanout: a capped pipe, usually 4 inches with a square nut on top, poking out of the ground within 10 feet of the foundation or set into the basement floor near where the main drain exits. That cap is the access point every plumber reaches for, and homes built before the 1970s sometimes lack one entirely, which adds $300–800 to any service call. From the cleanout the line normally runs in a straight shot to the street and ties into the main under the pavement. Your city can mark the tie-in from its records, and a plumber can trace the whole run with a camera and a sonde in about an hour.

Gravity does the work, so the pipe only has to stay round, sloped, and sealed. What it is made of decides how long that lasts. Vitrified clay, standard until the 1970s, arrives in 3 to 5 foot sections, and roots find every joint. Cast iron scales shut from the inside across 50 to 75 years. Orangeburg, a tar-impregnated wood fiber pipe laid roughly between 1945 and 1972, deforms into an oval and collapses after 30 to 50 years, which is why some mid-century blocks get replaced all at once. Modern PVC and ABS should reach 75 to 100 years. Failure shows first in the lowest fixtures, then as gurgling from a floor drain or tub when the washing machine empties, and finally as sewage backing into the basement, a cleanup that starts near $2,000 and rises fast.

Two habits cover it. Have the line cabled or jetted on a schedule if you own mature trees or clay pipe, which the cleaning interval guide generally sets at every 18 to 24 months; a rodding runs $200–500 and hydro jetting $400–900. Then scope it with a camera about every 5 years, and always before buying a house, per the camera inspection schedule. A $150–350 scope that catches a belly or a cracked clay joint before it backs up is the cheapest insurance in plumbing. The rest of the routine comes down to what you keep out of the drain: grease, wipes, and cat litter cause more blockages in newer pipe than roots do.