How to Locate Your Sewer Clean-Out Fitting

Main sewer pipe clean-out in ground

The Spruce / Ana Cadena

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. Though, not all houses connect to a city or municipal sewer; some connect to a cesspool.

The clean-out fitting is called the main house trap. It has two plugs for access, referred to as the house side and the street side. A stoppage in the house drain can be on the house side of the trap or street side. This makes a difference for which side of the trap plug you will open. If the source of the stoppage is in the house trap it is important to open the street side first (a general rule is to always open the street side first).

Main house traps are usually located along the front wall of the house when connected to the city or municipal sewer. For a cesspool it help to know if the cesspool is on the front or back of the house.

The main house trap 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.


A homeowner without plumbing experience should not try to clear the main house trap themselves. If the municipal or city sewer is the cause of the back-up, trying to clear out the main house trap can be disastrous and cause thousands of dollars in damages.

Tools and Supplies You Will Need

  • Flashlight (sometimes)
  • Rubber gloves
  • Pipe wrench


Find the Main House Trap

Finding the main house trap 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.

Open the Main House Trap

In most cases, opening the main house trap 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. Considerable 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. (Never apply heat to plastic pipes.)

The plugs, if they are brass will most likely never unscrew. They must be chopped out by a professional, without cracking the cast iron trap. If the trap has been accessed previously it is more likely than not that you have "fit-all" plugs. These type plugs are hammered down to put on and hammered in a horizontal motion to remove. Your best bet in this case is also to call a professional.

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.


When you start to open the plug and you see water or feel the pressure under the plug, it's time to call a professional. This means the stoppage in the line is the piping that travels outside the house. Once you pull the plug, your pit or house may fill with raw sewage in that localized area. Any sewage that collected at the previous low point will now show up here.

If you don't feel pressure or see water, you can remove the plug. (It should be noted that you may get a strong smell of sewer gas. This is not a healthy item to deal with.) Now that you've taken off the street-side plug, you can take off the house-side plug. If the stoppage is in the trap this plug will be under pressure. It is imperative you get this plug off fast. But, you must be careful because you don't want to get splashed with raw sewage nor have to work under water to try and get the plug off.

Clear the Stoppage

If you are successful then you can clear the stoppage in the trap with commercial-grade rubber gloves or a long tool.

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.