What is the 135 rule in plumbing?

What the Rule Actually Says

In Uniform Plumbing Code language, an additional cleanout is required for each aggregate horizontal change in direction exceeding 135 degrees in a drainage run. The word doing the work is aggregate: you add the turns along the run together rather than looking at any single fitting.

• Two 90-degree bends total 180 degrees. That exceeds 135, so another cleanout is required.
• A 45 plus a 90 totals exactly 135. That does not exceed the threshold, so no additional cleanout is triggered by that pair.
• Three 45s total 135 as well — again, at the limit rather than over it.

Note what it does not say. It does not prohibit a pipe from turning more than 135 degrees, and it does not cap the bends between access points. A run can turn as much as the layout requires; the code's response is to demand access so the run can be cleared when it blocks. Plenty of articles state the opposite, and homeowners occasionally arrive convinced their plumbing is illegal when it is merely under-served by cleanouts.

Why It May Not Apply to Your House

The 135-degree figure is Uniform Plumbing Code language, and the UPC is not the code family Colorado uses. The Colorado Plumbing Code is based on the International Plumbing Code, which handles the same problem differently: it requires a cleanout at each change of direction greater than 45 degrees in the building sewer, building drain and horizontal waste or soil lines, alongside its own spacing requirements along a run.

So in practical terms, a Colorado house is governed by a per-fitting rule rather than a cumulative 135-degree one, and the IPC's threshold is lower. Local jurisdictions can amend and can be more restrictive than the state minimum, and adopted editions change, so the authority for any specific job is the code edition your building department has adopted — which is one of the things a licensed contractor establishes when pulling the permit for the work.

Why Any of This Matters to a Homeowner

Cleanouts are the difference between a routine service call and an expensive one. With an accessible cleanout, clearing a main line is a straightforward job. Without one, the line has to be reached by pulling a toilet or cutting an access point into the pipe, which is the single biggest multiplier in both drain cleaning costs and sewer repair costs.

Two things follow. If your house has no exterior cleanout, adding one is worth considering on its own merits, and it is cheap to add while a trench is open for other work. And if you are being told your drainage needs an additional cleanout, that is usually a legitimate code requirement rather than an upsell. Cleanout installation is part of the scope on our sewer line repair page, and drain cleaning covers what having one does for routine maintenance.