8.1 Cleanout Sizing, Location, Clearances & Direction of Flow

8.1 Cleanout Sizing, Location, Clearances & Direction of Flow

Exam Focus: Sanitary drainage cleanouts are essential maintenance access points designed to facilitate the clearance of stoppages and mechanical rodding of piping networks. On the Michigan Journeyman Plumber examination, cleanout questions frequently appear in both the written code section and the practical isometric drawing examination. Candidates must know the exact trigger points requiring cleanouts under Michigan Plumbing Code (MPC) Section 708, the governing sizing rules (MPC Table 708.1.5), the mandatory working clearances for rodding equipment, and the proper fitting orientations relative to the direction of flow.

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1. Regulatory Purpose & Statutory Scope (MPC Section 708)

Under the 2021 Michigan Plumbing Code (MPC Section 708), sanitary drainage systems must be provided with cleanouts located so that all horizontal piping and vertical stacks can be readily reached with drain-cleaning cables and mechanical rodding tools. Stoppages in sanitary piping occur due to foreign objects, root intrusion, structural grease accumulation, or solids settling. Cleanouts ensure that these obstructions can be cleared without dismantling fixtures, cutting structural piping, or creating unsanitary spills within occupied tenant spaces.

All cleanout openings must be gas-tight, watertight, and fully accessible. Cleanouts must never be concealed behind permanent walls, beneath poured concrete slabs, or under finish materials without an approved removable access door or extension sleeve.

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2. Mandatory Cleanout Locations (MPC 708.1.1 – 708.1.5)

The code establishes specific physical locations where cleanouts must be installed across every drainage network:

+-----------------------------------------------------------------------------+
|                   MANDATORY CLEANOUT LOCATIONS (MPC SECTION 708)            |
+-----------------------------------------------------------------------------+
|                                                                             |
|  [1] BASE OF DRAINAGE STACKS                                                |
|      - At the base of every vertical soil or waste stack.                   |
|      - Located at or near the foot of the stack, above the bottom sweep.    |
|                                                                             |
|  [2] HORIZONTAL DEVELOPED LENGTH INTERVALS                                  |
|      - Every 100 feet of developed length on horizontal drainage runs.      |
|                                                                             |
|  [3] CHANGES OF DIRECTION GREATER THAN 45 DEGREES                           |
|      - At each horizontal change of direction exceeding 45 degrees.         |
|      - Exception: One cleanout covers aggregate turns within 40 feet.       |
|                                                                             |
|  [4] JUNCTION OF BUILDING DRAIN & BUILDING SEWER                            |
|      - Within 10 feet of the exterior building foundation wall.            |
|      - Two-way cleanouts or exterior cleanout risers permitted.             |
|                                                                             |
|  [5] UNDERGROUND PIPING MORE THAN 10 INCHES IN DIAMETER                     |
|      - Manholes at every major change and not more than 400 feet apart.     |
+-----------------------------------------------------------------------------+

1. Base of Vertical Stacks (MPC 708.1.2)

A cleanout must be provided at the base of each vertical waste or soil stack. The cleanout fitting is typically a wye or combination wye and 1/8 bend installed immediately above the bottom bend that transitions the vertical stack to the horizontal building drain or branch. This position allows a mechanical cable to be fed directly into the horizontal run where solids tend to drop out and accumulate.

2. Horizontal Developed Length Intervals (MPC 708.1.1)

Cleanouts on horizontal drainage pipes must be installed at intervals of not more than 100 feet (30,480 mm) of developed length. On long commercial or industrial building drains, cleanout risers (rodding wyes extended to the finished floor or outside grade) must be spaced every 100 feet along the entire length of the pipe run.

3. Changes of Direction Greater Than 45 Degrees (MPC 708.1.4)

A cleanout is required at each change of direction in horizontal drainage piping that is greater than 45 degrees (0.79 rad). For example, a 60-degree bend or a 90-degree bend (long-turn sweep) requires an accessible cleanout immediately upstream of the turn.

The 40-Foot Exception Rule (MPC 708.1.4 Exception): Where more than one change of direction exceeding 45 degrees occurs in a run of horizontal piping, only one cleanout is required for each 40 feet (12,192 mm) of developed length along that run. If a pipe makes two 90-degree turns within a 30-foot run, only one cleanout is required to serve both bends, provided the rodding cable can navigate the configuration without binding.

4. Junction of Building Drain and Building Sewer (MPC 708.1.3)

A cleanout must be provided at or near the junction of the building drain and the building sewer. The cleanout can be located:

• Inside or outside the building wall: Michigan's added MPC 708.3.5 allows the cleanout to be either inside or outside the building wall, brought up to finished ground level or to the basement floor level. The junction cleanout is not required where a cleanout on a 3-inch or larger diameter soil stack is located within a developed length of 10 feet of the building drain / building sewer connection.
• Outside the building: Located on the building sewer immediately exterior to the building foundation wall, extended to grade.
• Two-Way Cleanout: Installing an approved two-way directional cleanout fitting (or a pair of directional cleanouts installed back-to-back) at the building perimeter satisfies this requirement and allows mechanical rodding in both directions.

5. Large Underground Piping (More Than 10 Inches)

Michigan's added MPC 708.3.1 provides that for underground piping that is more than 10 inches in diameter, manholes must be provided and located at every major change of direction, grade, elevation, or size of pipe, or at intervals of not more than 400 feet (121 920 mm). Metal covers must be provided for the manholes and must be of sufficient weight to meet local traffic and loading conditions. Within buildings, manhole covers must be gastight and the manhole must be vented with not less than a 4-inch (102 mm) pipe.

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3. Cleanout Sizing Rules (MPC Table 708.1.5)

A common misconception among apprentice plumbers is that cleanouts must always match the size of the drainage pipe. Under MPC Section 708.1.5, cleanouts are sized according to the nominal diameter of the pipe being served, but the code caps the maximum required cleanout size at 4 inches.

+-----------------------------------------------------------------------------+
|                        CLEANOUT SIZING (MPC TABLE 708.1.5)                  |
+-----------------------------------------------------------------------------+
|                                                                             |
|  PIPE DIAMETER <= 4 INCHES:                                                 |
|  - Cleanout size MUST BE EQUAL to nominal pipe size.                        |
|  - Example: 2" pipe -> 2" cleanout; 3" pipe -> 3" cleanout; 4" pipe -> 4"   |
|                                                                             |
|  PIPE DIAMETER > 4 INCHES:                                                  |
|  - Cleanout size DOES NOT EXCEED 4 INCHES.                                  |
|  - Example: 6" pipe -> 4" cleanout; 8" pipe -> 4" cleanout; 10" pipe -> 4" |
+-----------------------------------------------------------------------------+

Master Sizing Table

Exam Trap Alert: If an exam question asks: "What is the minimum cleanout size required on an 8-inch commercial sanitary building drain?" the answer is 4 inches, NOT 8 inches! A 4-inch opening is sufficient to insert heavy-duty mechanical rodding blades, hydro-jetting nozzles, and sewer inspection cameras.

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4. Direction of Flow & Fitting Orientation (MPC 708.1.4)

Cleanouts must be installed to facilitate clearing stoppages in the direction of liquid waste movement:

                     APPROVED DIRECTIONAL CLEANOUT (WYE)

                             Cleanout Plug / Cap
                                     \
                                      \   <-- Rodding cable enters in
                                       \      direction of drainage flow
                                        \
  == UPSTREAM DRAIN ============\========\============ DOWNSTREAM DRAIN ==>
                                 \________\
                                (45° Branch)

1. Orientation Standard (MPC 708.1.9): The installation arrangement of a cleanout must enable cleaning of the drainage piping only in the direction of drainage flow.
2. Prohibited Backward Orientation: Cleanouts that open opposite to the direction of flow are strictly prohibited because rodding cables cannot make the severe reverse hairpin bend and will either bind, punch through the pipe wall, or fail to reach the obstruction.
3. Two-Way Cleanouts: A two-way cleanout tee (or double combination wye and 1/8 bend with opposing cleanout throats) is permitted near the building perimeter. This specialized fitting allows an operator to snake backward into the building drain toward internal fixture stacks, or forward downstream toward the public sewer main.

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5. Required Working Clearances & Physical Accessibility (MPC 708.1.10)

A cleanout is worthless if a service technician cannot maneuver a drain-cleaning machine in front of it. The Michigan Plumbing Code mandates strict physical working clearances in front of every cleanout plug:

+-----------------------------------------------------------------------------+
|                   UNOBSTRUCTED WORKING CLEARANCES (MPC 708.1.10)            |
+-----------------------------------------------------------------------------+
|                                                                             |
|  CLEANOUTS ON 6-INCH AND SMALLER PIPING:                                    |
|  - Minimum clearance = 18 INCHES (457 mm), measured perpendicular to and    |
|    from the face of the cleanout opening to any obstruction.                |
+-----------------------------------------------------------------------------+

                 WALL OR ENCLOSURE
                 +-----------------+
                 |                 |     <--- Minimum 18" clearance, measured
                 |                 |          perpendicular to the opening face
                 |      [ <------------ 18" Minimum -----------> ]
                 |                 |
                 |    +-------+    |             +-----------------------+
                 |    | PLUG  |    |             |  DRAIN CLEANING       |
                 |    +-------+    |             |  SNAKE MACHINE        |
                 |        |        |             |  & TECHNICIAN         |
                 |    [STACK]      |             +-----------------------+
                 |        |        |
                 +-----------------+

Concealed Cleanout Extensions

• In Walls: When drainage piping is concealed within finished wall cavities, cleanouts must be extended flush with the finished wall using a threaded cleanout adapter and an approved removable access cover plate, or housed within an accessible recessed wall box.
• Under Floors / Slabs: Cleanouts located below finished floors or concrete floor slabs must be extended up flush with the finished floor line. In finished floor areas, floor cleanouts must be equipped with an adjustable floor level housing, a scoriated (slip-resistant) cover plate, and a gasketed seal to prevent sewer gas egress and floor wash infiltration.
• In Crawl Spaces: If a cleanout is installed in an underfloor crawl space, the vertical clearance between the cleanout opening and the bottom of the floor joists or grade must comply with code, and an unobstructed crawlway path (minimum 22 inches by 30 inches) must lead from the access hatch to the cleanout.

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6. Cleanout Plugs & Traffic Specifications (MPC 708.1.6)

Cleanout plugs must seal the opening gas-tight and watertight while remaining removable for maintenance:

+-----------------------------------------------------------------------------+
|                         APPROVED CLEANOUT PLUG TYPES                        |
+-----------------------------------------------------------------------------+
|                                                                             |
|  RAISED-HEAD PLUG (SQUARE NUT)                                              |
|  - For walls, unfinished basements, mechanical rooms.                       |
|  - Raised square lug allows heavy pipe wrench engagement.                   |
|  - STRICTLY PROHIBITED in walkways, floors, and traffic zones.             |
|                                                                             |
|  COUNTERSUNK RECESS PLUG (FLUSH SOCKET / SLOTTED)                           |
|  - MANDATORY for finished floors, sidewalks, driveways, traffic corridors.  |
|  - Recessed socket or slot sits perfectly flush with surround.              |
|  - Eliminates trip hazards and vehicular shearing damage.                   |
+-----------------------------------------------------------------------------+

1. Approved Plug Materials: Cleanout plugs must be constructed of brass or plastic (PVC or ABS) matching the piping system. Plugs must have standard tapered national pipe threads (NPT).
2. Raised-Head Plugs: Feature an integral raised square nut or lug. Permitted only in exposed piping runs, unfinished utility spaces, or behind wall access panels where foot or vehicular traffic cannot contact the plug.
3. Countersunk Plugs: Feature a recessed square drive socket or slotted slot flush with the rim of the plug. Under MPC Section 708.1.6, countersunk plugs are mandatory in all floor assemblies, pedestrian walkways, aisles, driveways, and parking ramps. A raised-head plug in a walkway creates an unlawful tripping hazard and is vulnerable to being sheared off by pallet jacks or vehicle tires.

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7. Realistic Exam Application Scenarios

Scenario A: Warehouse Building Drain Extension & Spacing

Exam Scenario: A master plumber is reviewing the rough-in layout for a 280-foot straight horizontal building drain serving a logistics warehouse in Lansing, Michigan. The drain is constructed of 6-inch Schedule 40 PVC. The stack drops at the rear wall, and the drain exits through the front foundation wall to the public sewer.

How many cleanouts are required along this horizontal run, where must they be located, and what is their minimum nominal size?

Code Analysis:

1. Base of Stack: One cleanout is required at the base of the vertical soil stack at the rear wall (MPC 708.1.2).
2. 100-Foot Interval Cleanouts: Under Michigan's added MPC 708.3.1, all horizontal drains within buildings and building sewers must be provided with cleanouts located not more than 100 feet apart. For a 280-foot run, cleanout risers extended to the warehouse floor are required at developed lengths of 100 feet and 200 feet.
3. Building Drain / Sewer Junction: Under Michigan's added MPC 708.3.5, a cleanout is required near the junction of the building drain and the building sewer, either inside or outside the building wall and brought up to finished ground level or basement floor level.
4. Cleanout Sizing: Under MPC Table 708.1.5, cleanouts on piping larger than 4 inches are capped at a minimum of 4 inches. Even though the building drain is 6 inches in diameter, the contractor is legally permitted to install 6-inch by 4-inch wye cleanouts with 4-inch countersunk brass or PVC plugs.
5. Total Cleanouts: 4 cleanouts minimum along the run (Base of stack, 100 ft, 200 ft, and exit junction).

Scenario B: Directional Change on an Underground Branch

Exam Scenario: An underground 3-inch horizontal branch drain in a commercial kitchen changes direction twice within a developed length of 25 feet: first by a 45-degree fitting, then 10 feet later by a 90-degree long-turn sweep. The branch is buried beneath a poured commercial quarry tile floor.

What cleanouts are mandated, what type of plug must be specified, and what clearance must be provided?

Code Analysis:

1. Directional Change Rule: The 45-degree fitting does not exceed 45 degrees, so it does not trigger a cleanout. The 90-degree long-turn sweep exceeds 45 degrees, triggering the requirement of MPC 708.1.4.
2. Application of 40-Foot Exception: Even though multiple bends occur, the total developed length is only 25 feet (less than 40 feet). Therefore, a single cleanout riser located upstream of the 90-degree turn satisfies the code.
3. Plug Specification: Because the cleanout terminates in a commercial kitchen finished tile floor, MPC Section 708.1.6 requires a countersunk plug mounted flush with the finished tile floor to prevent tripping and allow cart traffic.
4. Working Clearance: Because the cleanout serves 6-inch or smaller piping, MPC Section 708.1.10 requires not less than 18 inches of clearance from, and perpendicular to, the face of the cleanout opening to any obstruction.