How to Locate Your Sewer Clean-Out Fitting

Sewer cleanout


More often than not, a clog in a toilet, sink, or other plumbing fixture will be solved by the use of a plunger or drain snake used right at the fixture itself. Sometimes, though, the main sewer line itself that carries waste from the house to the city sewer system can get clogged. Many homeowners have experienced the unpleasant symptom of this—a floor drain backing up so that foul, sewage-laden water spreads over the floor.

How a Main Clean-out Fitting Works

The main sewer line is a large-diameter pipe that pipe that carries waste from every sink, toilet, and shower in your home, through branch drains that connect into it. When it gets clogged, every fixture in your home is affected, so it is a problem that just can't wait. When you call a plumber or sewer specialist to clear the stoppage, you almost always will be asked if you have a clean-out fitting. The cost of the service call will be determined in part by your answer. Augering the main sewer line is fairly easy if there is an accessible clean-out; it's much harder (and more expensive) if the plumber has trouble getting at the sewer line. 

The clean-out fitting can take a number of different appearances, but most typically it is a 3-inch, 4-inch, or 6-inch diameter pipe with a visible plug or that can be unscrewed with a wrench. This plug is usually a threaded fitting, but sometimes is a bell-shaped cap, or (more rarely) a rubber bonnet secured with a pipe clamp. Sometimes the main clean-out is located in the floor, while other times it is a wye-fitting or tee fitting mounted at the base of the main soil-stack in the house. In larger homes where more than one main line runs out to the municipal sewer service, it's possible there will be more than one sewer clean-out fitting. In warmer climates, the clean-out fitting will be located outside the house, usually close to the foundation, and will be set at ground level.

Causes of Main Sewer Line Clogs

Given its large diameter, a main sewer line does not get clogged all that often. Clogs in smaller-diameter branch drains are much more common than blockages in main sewer lines. It is possible for blockages to occur if large amounts of debris are flushed down the drain, but more often it occurs because of a buildup of sludge in old main drain pipes. With the diameter of the pipe gradually narrowed over time, it becomes more likely that the pipe can become clogged by relatively small debris. This is often cured by augering with a larger version of the drain snakes that are typically used to clear branch drain clogs.

Main drain clogs can also occur if tree roots in the yard penetrate the joints between pipes and block the sewer pipe. In this instance, a sewer professional usually clears the blockage with a special auger with cutting blades. Homeowners who have experienced this once are well advised to have their sewer lines cleared every few years as a preventive measure. Finally, a blockage can occur when old sewer lines collapse completely, a problem that occurs mostly with old pipes made of clay or cast iron. This is no easy problem to fix, as it usually involves digging up the yard and replacing a portion or the entire run of drain pipe from the house to the municipal sewer main.

Most often, though, clearing sewer line blockages begin at the main clean-out fitting.

Tools and Supplies You Will Need

  • Flashlight (sometimes)


Finding a clean-out is not always easy. It is very often found in a utility area, but since it is used infrequently, it's common for homeowners to forget about it and gradually hide it behind shelving, benches, or stored items. You may need to peer about with a flashlight to find it.

In colder climates, the main clean-out is almost always located inside the house as a protection against freezing. It is often in a basement. You may see a 3-inch- or 4-inch-diameter pipe stub extending up out from the slab floor. The pipe may be made of cast-iron or plastic; more rarely it might be brass or even copper. The stub-out will have a screw-in plug with a square-head lug on it, which is your main drain access. When a clog or stoppage in the main drain line occurs, this will be where you access the line to auger it clear of obstructions.

If there is no floor clean-out fitting, look for it in a wye (Y) fitting, sanitary tee fitting, or cross tee fitting at the base of the vertical soil stack at the point where it goes down beneath the floor. This fitting also will have a plug fitting with a wrench lug on it.

In slab homes in cold climates, the main clean-out may be in a utility room or attached garage. One way to find it is to visualize a line from a floor drain running out toward the municipal sewer lines, which usually lie beneath the street. In most cases, the main clean-out will be located at some point along this line from floor drain to street. In some instances, the clean-out fitting will be flush-mounted in the floor, but it may also be a raised stub-out pipe. Either way, there is usually a square lug in the center of a plug, used to twist the plug with a pipe wrench.

In warmer regions, the main clean-out is more often on the exterior of the house. You will need to carefully look at all sides of the house to find the sewer clean-out because there could be more than one, and they can be obscured by landscaping. Often, the main clean-out is set into the ground or a concrete slab, with a hinged round cover. Or, it may be a raised pipe with a screw-in plug.

Opening the Main Clean-out

In most cases, opening the clean-out fitting will involve using a large pipe wrench to grip the lug in the center of the plug and twisting it counterclockwise to unscrew the plug. This can be fairly easy if the clean-out is plastic (even a large pair of channel-lock pliers may do the trick), or it can be quite difficult if the pipes are cast-iron and the fitting has not been opened in a long while. Considerably force might be necessary in this instance. Stubborn metal clean-out plugs can be sometimes be loosened if you apply heat to the metal pipe hub around the plug, which slightly expands the metal and loosens the fit. (Obviously, never apply heat to plastic pipes). After your drain work is complete, coat the threads of the plug with pipe dope before reinserting it. This will make it easier to remove the plug in the future.

Less frequently, the clean-out may be covered by an expandable plug that is loosened by twisting a screw in the center of the plug. Even more rarely, the clean-out fitting may be covered by a rubber bonnet that is removed by loosening a pipe clamp that secures the bonnet to the hub of the fitting.