What Is a Clean Out?
In residential and commercial plumbing, a cleanout (or sewer cleanout) is an accessible pipe fitting with a removable threaded cap that provides direct access to the main drain-waste-vent (DWV) system and underground sewer lateral line. Located either inside the home (in basements, utility rooms, or crawl spaces) or outside in the yard along the foundation wall, the cleanout allows plumbers to insert motorized drain cleaning snakes, high-pressure hydro-jetting nozzles, and sewer inspection cameras directly into the main sewer pipe without having to dismantle toilets, cut drywall, or work from hazardous roof vents. Having an accessible, code-compliant cleanout is crucial for clearing stubborn tree root intrusions, grease clogs, and sewer line backups before waste backs up into residential living spaces.
Plumbing Cleanout Types, Locations, and Anatomy
Plumbing codes mandate specific cleanout configurations based on pipe diameter, total run length, and directional changes. Under the International Plumbing Code (IPC) and Uniform Plumbing Code (UPC), cleanouts are constructed using a 45-degree wye or sweep fitting rather than a sharp 90-degree tee. This directional angle guides motorized sewer cables smoothly in the direction of wastewater flow toward the municipal sewer main or septic tank.
Cleanouts are typically categorized by their physical placement: main sewer line cleanouts, branch line cleanouts, and fixture cleanouts. Outdoor main cleanouts usually feature a 3-inch or 4-inch PVC or ABS pipe rising flush with ground level, capped with a raised square nut or recessed brass plug. In older homes, cleanouts may consist of heavy cast iron pipes with lead-sealed brass plugs. Dual two-way cleanouts feature two adjacent pipes: one angled toward the street to clear municipal lateral blockages, and one angled back toward the house to service interior drains.
The table below outlines standard plumbing cleanout varieties, material specifications, and optimal operational applications.
| Cleanout Category | Pipe Diameter & Material | Physical Location | Primary Maintenance Function |
|---|---|---|---|
| Outdoor Main Cleanout | 3" to 4" Schedule 40 PVC/ABS | Yard near foundation or sidewalk | Accesses main sewer line to municipal main |
| Two-Way Cleanout (U-Trap) | Double 4" wye fitting pipes | Exterior perimeter landscaping | Allows snaking both toward house and street |
| Indoor Base of Stack | 3" to 4" Cast Iron or PVC | Basement wall, crawlspace, garage | Services vertical drainage stacks from upper floors |
| Under-Sink Branch Cleanout | 1.5" to 2" PVC threaded tee | Inside vanity cabinet or behind sink | Clears kitchen grease or bathroom hair clogs |
| Property Line Cleanout | 4" PVC with cast iron lid | Near street curb / easement line | Demarcates homeowner lateral from city sewer |
| Roof Vent Stack Cleanout | 2" to 4" Open vent penetration | Top of residential roof | Emergency snaking point when ground caps stuck |
Building codes require a cleanout at the junction of the building drain and sewer, and every 100 feet of horizontal sewer piping.
How Plumbers Clear Main Line Clogs via the Cleanout
When multiple plumbing fixtures back up simultaneously—such as sewage bubbling into a shower stall when a toilet is flushed—the blockage is located inside the main sewer line. Opening the sewer cleanout relieves hydrostatic pressure, allowing standing water to drain harmlessly outside rather than overflowing onto indoor carpets and hardwood floors.
Once the cleanout cap is loosened and removed, technicians introduce specialized diagnostic and clearing machinery. A high-definition sewer scope camera with an integrated 512 Hz locating sonde is inserted to pinpoint pipe collapses, bellies, or tree root penetration. Next, a heavy mechanical drum auger with a root-cutting c-cutter blade or a 4,000 PSI hydro-jetter is fed down the cleanout, scouring grease buildup and root masses from the interior pipe walls.
The table below compares diagnostic and clearing techniques deployed through sewer cleanouts.
| Drain Clearing Method | Machinery Deployed | Effective Against | Key Operational Advantage |
|---|---|---|---|
| Continuous Drum Snake | Electric motorized steel cable | Tree roots, feminine hygiene products, rags | Slices roots and retrieves physical obstructions |
| High-Pressure Hydro-Jetting | 3,500 - 4,000 PSI water jet nozzle | Heavy grease, sludge, scale, sand, mud | Restores original pipe diameter 360 degrees |
| Fiber-Optic Sewer Scope | Color camera head with LED lights | Cracked pipes, offsets, root intrusion, sags | Provides real-time video diagnosis on monitor |
| Trenchless CIPP Lining | Epoxy-soaked felt liner bladder | Fractured, leaking, or aged clay/iron pipes | Repairs broken sewer pipe without yard excavation |
Always wear heavy gloves, eye protection, and stand to the side when unscrewing a cleanout cap during an active backup to avoid sewage spray.
How to Locate and Open a Sewer Cleanout in 5 Steps
Follow this practical sequence to find your home's main cleanout and safely relieve sewer line backup pressure.
Search Along Exterior Foundation Walls
Walk the exterior perimeter of your house near bathrooms or the kitchen, looking for a 3- to 4-inch capped pipe protruding from soil or concrete.
Check Basements, Crawl Spaces, and Garages
If not found outdoors, inspect basement walls, utility closets, or crawlspaces for an angled cast iron or PVC fitting with a square nut.
Clear Away Soil and Overgrown Shrubbery
Carefully dig away accumulated mulch, dirt, or landscaping vegetation that may have buried an outdoor flush ground cap.
Slowly Loosen the Threaded Cleanout Cap
Use a large pipe wrench or cleanout plug wrench to slowly loosen the cap counter-clockwise, listening for pressurized water hissing.
Insert Drain Auger or Call a Licensed Plumber
Once drainage subsides, feed an electric drain snake down the line in the direction of the sewer or call a licensed drain technician.
Frequently Asked Questions (7 Questions Answered)
Q1: Where is the sewer cleanout usually located?
The main cleanout is typically located outside near the foundation wall closest to the primary bathroom, flush in the front lawn near the sidewalk, or in the basement.
Q2: What happens if you open a cleanout during a backup?
If sewage is backed up above the cleanout level, removing the cap will release pressurized wastewater onto the ground outside, saving indoor living areas from flooding.
Q3: Can you snake a sewer line from a cleanout yourself?
Yes, homeowners can rent a heavy-duty motorized sewer snake from hardware stores to clear simple blockages, though severe root intrusions usually require professional hydro-jetting.
Q4: What does a cleanout cap look like?
It is a round, threaded plastic (white or black) or brass cap featuring a raised square nut or a recessed square drive slot on top.
Q5: Why do some houses have two cleanout pipes outside?
Two adjacent pipes represent a two-way cleanout system: one pipe angles toward the municipal sewer main, while the other angles back toward the home's plumbing.
Q6: What is the difference between a cleanout and a sewer trap?
A cleanout provides direct straight access into the pipe, while a trap features a water-holding U-bend designed to prevent sewer gases from entering the structure.
Q7: How much does it cost to install a sewer cleanout?
Installing a new outdoor sewer cleanout costs between $1,200 and $2,500 depending on excavation depth and whether the pipe is cast iron, clay, or PVC.
Final Thoughts & Key Takeaways
In conclusion, understanding what is a clean out? provides essential clarity, practical strategies, and actionable advice. By incorporating these foundational insights, adhering to verified safety guidelines, and following structured best practices, you ensure reliable, long-term outcomes while preventing common mistakes. Stay informed, consult certified professionals when needed, and maintain consistent quality care.