Where are sewer cleanouts required for an ADU in California?

Under the 2025 California Plumbing Code, your ADU's drain piping needs a cleanout at the upper end of each horizontal drain, another for every 100 feet of run, and one wherever the line's horizontal turns add up to more than 135 degrees (Section 707.4). The building sewer that carries waste from the ADU to the tie-in needs its own cleanout where it leaves the building, plus more at the same 100-foot and 135-degree points (Section 719.1).

Inside the ADU: drainage piping (707.4)

• A cleanout at the upper terminal of each horizontal drainage pipe.
• For runs longer than 100 feet of developed length, an additional cleanout for each 100 feet or fraction of 100 feet.
• An additional cleanout for each aggregate horizontal change in direction greater than 135 degrees.

The code lists exceptions. You can skip a cleanout on a horizontal drain shorter than 5 feet unless it serves sinks or urinals, and on pipe installed at 72 degrees or less from vertical. Piping above the lowest floor generally doesn't need one, except the building drain, its horizontal branches, kitchen sinks, and urinals. An approved two-way cleanout near the junction of the building drain and building sewer can stand in for the upper-terminal cleanout.

Outside: the building sewer (719.1)

• Place a cleanout inside the building near where the building drain meets the building sewer, or outside at the lower end of the building drain, extended to grade.
• Add cleanouts at intervals of no more than 100 feet in straight runs.
• Add one at each point where the horizontal change in direction adds up to more than 135 degrees.

A detached ADU at the back of a lot often has a long building sewer with a couple of bends on the way to the house lateral, so count the turns before you assume one cleanout is enough.

Making cleanouts usable

• Cleanouts must open in the direction of flow or at right angles to it (707.5).
• They must be readily accessible (707.8). A cleanout trapped under tile or a cabinet floor fails the point of having one.
• Leave clear working space in front: 18 by 18 inches for pipe 2 inches and smaller, 24 by 24 inches for larger pipe (707.9).
• Under-floor cleanouts must extend to or above the finished floor, or outside the building, where there is less than 18 inches of vertical clearance (707.9).
• Covers in driveways or floors that carry loads must be load-rated to ASME A112.36.2M (707.4.1).

Garage conversions and local rules

In a slab-on-grade conversion, plan cleanout locations before the slab is cut so they land at an exterior wall or an accessible spot rather than under finished flooring. Your sewer agency may also have lateral standards of its own, including where cleanouts go, and some cities amend these sections. Check both before you finalize the layout.

What it means for your plumbing plan

Your plans should show every cleanout on the DWV layout and the site plan, with its size, type (end-of-line or two-way), and access. That is what lets your plumber install them in the right places and your inspector sign off. See why the DWV system must be shown on plans, sewer lateral inspections, and our garage conversion MEP plans.

Sources: gocodebook.com, gocodebook.com, gocodebook.com.