UPC 706: Changes of Direction in Drainage Piping

Section 706 is titled Changes in Direction of Drainage Flow. It splits the rule by the kind of turn and lists approved fittings for each:

706.2 Horizontal to Vertical 706.3 Horizontal to Horizontal 706.4 Vertical to Horizontal

Under 706.1, every change of direction has to use an approved fitting with the right sweep. A sweep is how gently the fitting curves. A long-sweep fitting turns the flow in a slow arc. A short or tight fitting turns it sharply.

Waste water carries solids. Solids need speed and a smooth path to stay in the stream. A sharp turn slams the flow into the pipe wall. That kills speed, stirs up turbulence, and lets solids drop out and collect. A long-sweep fitting bends the flow gently, so the water keeps its speed and carries solids through. This is why one elbow can clog again and again when a tight fitting was used where a sweep belonged.

When a horizontal branch drops into a vertical stack, gravity is already pulling the water down. The code allows a tighter fitting here, such as a sanitary tee, because the drop does the work. This is the one turn where a short-radius fitting is acceptable. The joint that ties each fitting to the pipe follows UPC 705 on drainage joints.

These two turns are the hard ones. The water has to change direction while it stays in a nearly level pipe, or it drops down a stack and then has to flatten out. Section 706 calls for a more gradual sweep here than it allows for a horizontal-to-vertical turn. That means long-sweep quarter bends, wye branches, or a combination wye and eighth bend, not a plain tight quarter bend. The base of a stack is the classic trouble spot. Water falls fast, then has to turn and run flat, so a long sweep is needed to carry it without a backup.

If a drain clogs at the same elbow over and over, the fitting may be too tight for that turn. That is a rough-in problem, not something a snake fixes for long. The repair means opening the wall or slab and swapping the fitting for a proper sweep. Turn geometry works together with pipe grade, so see how much slope a drain pipe needs and why the same drain keeps clogging. If a fixture like a toilet keeps backing up, read why a toilet keeps clogging. Our drain cleaning service can camera the line to find a bad fitting.

UPC Section 706 is part of the Uniform Plumbing Code. IAPMO publishes it and holds the copyright, so only the section headings and short notes are shown here. Phoenix enforces the 2024 UPC with local amendments. Read the section on the UPC viewer at UpCodes, review the official code at IAPMO, or confirm local amendments with the City of Phoenix Planning & Development Department at phoenix.gov/pdd.