Washington's journey-level plumbing exam is written against the 2015 UPC, not the 2021 UPC the state currently enforces on the job. In Washington's 2015-edition text of Table 703.2 (note 4, the water-closet limit), how many water closets or six-unit traps are permitted on a horizontal branch or drain?
Not quite. The answer is D: 3
Washington's 2015-edition Table 703.2 note — printed in WAC 51-56-0700 as it stood before July 1, 2020 — allows only four water closets or six-unit traps on a vertical pipe or stack and not more than three on a horizontal branch or drain, a tighter limit than the row's raw DFU capacity would give. (An exception let a single-family addition or alteration put four 1.6 gpf closets on a 3-inch horizontal waste when a 4-inch waste was not readily available and the authority approved.) The 2021 UPC that Washington enforces since March 15, 2024 replaced the split with a single cap of five water closets or five six-unit traps regardless of orientation, so a candidate who studies from a current book will get this exam question wrong.
Reference: WAC 2015 51-56-0700, Table 703.2 note 4 (2015-edition amendments) (Table 703.2 — water closet limit (exam edition))
Checked against the official text
Edition conflict: the 2015-basis text allows 4 vertical / 3 horizontal; the 2021 code in force since 2024-03-15 allows 5 total.