7.2 Cleanout Locations, Sizing & Clearances

7.2 Cleanout Locations, Sizing & Clearances

Quick Answer: 248 CMR 10.08(3) (12/8/2023) places cleanouts no more than 50 feet apart on horizontal drainage and branch piping 4 inches or less, and no more than 100 feet apart on horizontal piping over 4 inches. Add a cleanout at or near the base of each vertical storm conductor, waste, or soil stack, at each change of direction of the building drain, and at each change of direction greater than 45° on horizontal waste, soil, and branch lines. Size matches the pipe up to 4 inches and is not less than 4 inches on larger pipe. Leave 18 inches of working room on 3-inch and larger cleanouts and 12 inches on smaller than 3 inches. Do not pull spacing from an IPC 100-foot table.

PSI lists Cleanouts as two items. The Board still writes a full installation rule. A journeyman who can snake a stoppage but cannot cite 50 versus 100, 18 versus 12, or the 5-foot outside option will miss those items. This section is 248 CMR 10.08(3), with one related kitchen-sink note from 10.15 that shows up next to trap work.

Developed-length intervals — the number pair that is not IPC

248 CMR 10.08(3)(a) is explicit. Cleanouts shall be placed no more than 50 feet apart in all horizontal drainage piping and branch drain piping which is four-inch in diameter or less. On horizontal piping which is over four inch in diameter, cleanouts shall not be more than 100 feet apart. Example 4 is the Board’s picture of that maximum distance.

IPC horizontal-drain language that many candidates memorized uses 100 feet as the ordinary interval for building drains. Massachusetts does not. A 3-inch or 4-inch house building drain is on the 50-foot clock. A 6-inch horizontal is on the 100-foot clock. If a PSI stem says “3-inch horizontal waste, 80 feet between cleanouts,” that run already exceeded 50 feet. Do not “correct” it with an IPC 100-foot memory.

Measure developed length along the pipe, including offsets, not a straight-line tape across the basement. A 48-foot run with two 45s that add 8 feet of developed length is not “under 50 feet” on the plan dimension alone.

Where else a cleanout is required

Intervals are not the whole list. 248 CMR 10.08(3) also requires accessible cleanouts at:

Read the change-of-direction bullets as two different tests. The building drain gets a cleanout at each change of direction — the text does not add “greater than 45°” on that building-drain bullet. Horizontal waste, soil, and branch lines use the greater than 45° trigger. A 22½° kick on a 2-inch lavatory branch is not automatically a 10.08(3)(d)2 cleanout. A 90 on that same branch is. A 22½° on the building drain still sits on the “each change of direction of the building drain” bullet.

Underground drainage. When a cleanout is installed on underground drainage piping, extend it vertically to or above finished grade, or extend it to an accessible location immediately outside the building (Example 9).

Inaccessible interior cleanouts. For buildings with concrete floors (slabs) or with less than 36 inches of crawl space under the floor, or where a cleanout is not easily accessible, the building-drain cleanout may be installed outside, not more than 5 feet beyond the foundation wall (10.08(3)(h), Examples 8 and 9). That is permission with a distance cap, not a command to skip the interior cleanout when you have a usable basement.

Scenario. A Lowell slab ranch has a 4-inch building drain that turns 90° just inside the foundation and then runs 40 feet to the stack. You still owe: a foundation cleanout with a straight shot to the sewer (outside within 5 feet is available because it is a slab), a cleanout at that 90 on the building drain, a cleanout at or near the stack base, and 50-foot spacing on that 4-inch horizontal. The 40-foot run between the 90 and the stack does not by itself exceed 50 feet, but the direction change and the stack base are separate triggers.

Plug hardware, direction of flow, size, and working clearance

248 CMR 10.08(3)(b) — cleanout plugs shall be brass or plastic, meet the latest testing standards, and have raised or countersunk square or hexagon heads. If a tripping hazard may exist, use only a countersunk head. Plastic plugs shall be of the same material as the piping they connect to. Do not put a PVC plug in an ABS fitting and call it good.

Direction of flow (10.08(3)(i)). Every cleanout shall open in the direction of flow of the drainage line or at right angles thereto. A cleanout that faces upstream so the snake has to make a U-turn is not the installation 10.08 describes.

Size (10.08(3)(j)). Cleanouts shall be of the same nominal size as the pipes up to 4 inches and not less than 4 inches for larger piping. A 2-inch branch gets a 2-inch cleanout. A 3-inch waste gets 3 inches. A 4-inch building drain gets 4 inches. A 6-inch or 8-inch line still gets at least 4 inches, not a 2-inch “because we can get a small snake in.” IPC notes that let a stack cleanout shrink one size are not 248 CMR 10.08(3)(j).

Clearances (10.08(3)(k), Example 10).

• 3-inch or larger: not less than 18 inches for clearing stoppages.
• Smaller than 3 inches: 12-inch clearance.

IPC required-clearance tables that use 18 inches for 6-inch-and-smaller and 36 inches for larger pipe are a different code. Massachusetts splits at 3 inches, and the small-pipe number is 12 inches, not 18.

Keep them usable (10.08(3)(l)). Do not cover plugs with cement, plaster, or any other permanent finishing material. Where concealment is necessary, a covering plate or access door must allow ready access for removal. Finished tile over a floor cleanout with no plate is a failed inspection, not a “hidden equivalent.”

Equivalents, prohibited use of the opening, manholes, kitchen sinks

Cleanout equivalent (10.08(3)(m)) may be satisfied by:

1. a fixture trap that incorporates a union connection;
2. a fixture with an integral trap; or
3. roof-drain covers that are readily removable without disturbing concealed rough piping.

That equivalent is for the location it actually serves. A union tailpiece under a lavatory does not replace the building-drain foundation cleanout or the stack-base cleanout.

Connections to cleanouts prohibited (10.08(3)(n)). Do not use a cleanout opening for new or additional plumbing except where another end-cleanout of equal access and capacity is provided. Tapping a cleanout tee to add a basement sink, then leaving no equivalent end cleanout, is the classic violation.

Manholes for large pipes (10.08(3)(o)). For underground and “dedicated system” piping that is over 10 inches in diameter and outside a building, manholes are provided at every change of size, direction, grade, or elevation and at intervals of not more than 350 feet, except when the total developed length of the drain is less than 150 feet, in which case cleanouts may be installed at 75 intervals. Teach those figures as 10.08 prints them. Do not substitute an IPC manhole spacing table.

Related kitchen-sink rule (248 CMR 10.15(8)(c), not 10.08). A full-size cleanout shall be installed under all kitchen sinks, except a two-piece kitchen-sink trap that may be disassembled in lieu of that cleanout. The residential kitchen branch is not less than 1½ inches, and a kitchen sink shall not waste into any horizontal drain smaller than 3 inches that already receives a flat-bottom fixture. Rough the drain high enough to accept a disposer. That 10.15 cleanout sits next to the 10.08 trap on every kitchen rough.

Do not schedule, size, or clear cleanouts from IPC Chapter 7 or IRC P3005 tables. Massachusetts intervals, the 3-inch clearance split, same-size-up-to-4-inches, the 5-foot outside cap, and the 36-inch crawl test are 248 CMR 10.08(3).

Official resources

• 248 CMR 10.08(3) Drainage Pipe Cleanouts (Cornell LII) — 50 ft / 100 ft, 18 in. / 12 in., 5 ft outside, manholes
• 248 CMR 10.08 (UpCodes) — Examples 4 through 10
• 248 CMR 10.15(8)(c) Kitchen Sink Wastes — full-size cleanout under residential kitchen sinks
• 248 CMR 10.00 (Mass.gov) — 12/8/2023 official posting