Sewer cleanout: what it is, where to find yours, and what if there isn't one

Every sewer line eventually needs clearing or inspecting, and the cleanout is the door. It's a short vertical pipe, usually 3 or 4 inches across, that tees into the main sewer line and rises to the ground surface or the basement floor, closed with a threaded plug.

With a cleanout, a plumber can feed a drain cable, a jetter hose or a camera straight into the main line in minutes. Without one, they have to go in through a roof vent or remove a toilet, which takes longer, costs more and reaches the line less effectively.

You'll see it written several ways — sewer clean out, sewer line cleanout, main line cleanout, or just plumbing cleanout. They mean the same fitting when it's on the main line. Strictly, "plumbing cleanout" covers every access plug in the drain system, including the small ones under sinks and at the base of each stack; the sewer cleanout is the big one on the line that leaves the house.

Plumbing codes require a cleanout near the point where the building drain inside becomes the building sewer outside, brought up to finished grade or the basement floor, so that's where to look first.

1. Walk the outside of the foundation, especially on the side nearest the bathrooms and the kitchen, and on the side facing the street. Look for a capped pipe a few inches above the ground, or a small ground-level box with a lid.
2. Check near the property line or the front of the lot. Many homes have a second cleanout there, and some cities require one.
3. Look indoors where the main drain leaves the house: in the basement or crawl space near the wall facing the street, in a utility room, a garage, or near a floor drain.
4. Check under bushes, mulch and grass along that side of the house — cleanouts are often buried by landscaping or cut down flush with the lawn.
5. Ask the previous owner, a neighbour with the same house design, or look for a previous plumbing invoice or sewer scope report, which usually notes the access point.
6. Still can't find it? A plumber can send a camera with a transmitter in through a vent or a toilet and locate the line and any buried cleanout from above.

Many homes have one of each, and they do slightly different jobs. An outside sewer line cleanout — the capped pipe sticking out of the yard near the foundation or by the property line — opens onto the building sewer that runs to the street. It's the one plumbers prefer, because a clog can be cleared without bringing equipment or sewage into the house.

A cleanout inside the house sits on the building drain, usually low on a basement wall, in a crawl space or in a utility room. It's common in colder regions, where an outdoor riser could freeze or where the main drain leaves through a basement wall well below grade. It works, but opening it on a backed-up line releases sewage indoors — which is why you should never open an indoor cleanout while drains are backed up.

• A white or black plastic pipe with a threaded cap that has a square or hexagonal nub on top for a wrench — the most common modern cleanout.
• In older homes, a cast iron fitting with a brass or iron plug, often in the basement on the main drain.
• A small round or square ground box with a metal or plastic lid, used where a cap would be hit by a mower.
• A two-way cleanout: two caps side by side, or a single cap over a fitting that opens toward both the house and the street.
• Not to be confused with an irrigation box, a gas or water meter, or a septic tank riser — those have different lids and are often labelled.

Most US jurisdictions adopt a version of the International Plumbing Code or the Uniform Plumbing Code, with local amendments, so details vary. The International Plumbing Code, for example, requires cleanouts:

• Near the junction of the building drain and the building sewer, inside or outside the wall, brought up to finished ground level or the basement floor.
• On building sewers at intervals of not more than 100 feet.
• At each change of direction greater than 45 degrees in the building sewer and building drain (with some relief where several bends occur close together).
• At the base of each vertical soil or waste stack.

A one-way cleanout opens toward the street, which covers most clogs. A two-way cleanout opens in both directions, so a plumber can also reach the section back toward the house without going through a fixture — worth the extra when the line is being dug up anyway.

Installation ranges from Angi and plumbing contractor cost guides (2026). Depth, distance to the line and concrete over it drive the price.

Older homes often don't. It isn't a defect you have to fix immediately, but every clog becomes more expensive and slower to clear, and some jobs — camera inspections, jetting, lining — are much harder without one.

Installing a cleanout pays for itself after a couple of main-line calls, because a plumber can then clear the line from outside in a short visit. The ideal time is whenever the line is being dug up for another repair.

Clearing a main line with and without a cleanout→

• A cracked or missing cap: an open pipe into the sewer lets in rainwater, debris and pests, and lets sewer gas out. Replace it.
• A cap cut down by a mower or buried under a new patio: have it raised or fitted with a ground box.
• Rainwater or yard drainage directed into a cleanout: most cities prohibit it, because it overloads the sewer.
• Sewage coming out of the outdoor cleanout: the line is blocked downstream of it — stop using water and call a plumber, or the utility if neighbours are affected.
• A seized plug: don't force it with heat or a hammer on old cast iron; a plumber can cut and replace it.