If you searched for the "135 rule" in plumbing, you've probably seen an answer that sounds like it applies everywhere. It doesn't. It depends on which plumbing code your city uses.
What the 135 rule is
The Uniform Plumbing Code (UPC) requires an extra cleanout in a horizontal drain line for each time the line's turns add up to more than 135 degrees.
For example: three 45-degree bends in a row add up to 135 degrees. Turn again past that, and the UPC calls for another cleanout.
The reason is access. A cleanout is an opening a plumber can use to get a cable, jetter or camera into the line. The more a pipe turns, the harder it is to push a tool through it from far away. The rule makes sure every stretch of pipe can still be reached.
It's a cleanout rule, not a rule about venting or traps.
Mesa doesn't use the UPC
Mesa uses the International Plumbing Code (IPC), the 2024 edition since January 8, 2026, like many Arizona cities. The IPC handles this differently:
- A cleanout at each change of direction greater than 45 degrees in the building sewer, building drain and horizontal waste or soil lines.
- Where a run has more than one change of direction, one cleanout for each 40 feet of developed length can cover it.
So in Mesa, the "135 rule" isn't the rule. If you're planning work, go by the IPC as Mesa adopted it, along with the city's amendments, and check with Mesa Development Services.
Why this matters to a homeowner
You probably won't be laying out drain lines yourself. But cleanouts are why a clog can be cleared quickly, and why a camera can find a problem without opening a wall or floor.
- Know where your main sewer cleanout is.
- If you're remodeling, make sure new drain lines keep a cleanout reachable.
- Our $99 drain cleaning offer is for main-line cleaning with an accessible cleanout.
Better fittings, better flow
Whichever code applies, plumbers use gentle turns on horizontal drains: long-sweep elbows or two 45s instead of a sharp 90, and a wye where lines join. Gentle turns keep waste moving and make the line easier to clean.
Drains that keep clogging? See drain cleaning and hydro jetting, or call OX Plumbing 24/7.