In Washington's 2015-edition text of Table 703.2 (note 4, the water-closet limit) — the edition the journey-level exam is written against, not the 2021 UPC enforced on the job — how many water closets or six-unit traps are permitted on a vertical pipe or stack?
Not quite. The answer is B: 4
Washington's 2015-edition Table 703.2 note — printed in WAC 51-56-0700 as it stood before July 1, 2020 — allows four water closets or six-unit traps on a vertical pipe or stack, one more than the three allowed on a horizontal branch. The 2021 UPC that Washington enforces since March 15, 2024 replaced the split with a single cap of five regardless of orientation, so a candidate trained on the current book tends to get this backwards. (The 2021 UPC also added an unrelated allowance of up to 8 public lavatories on a 1½-inch branch, which has no equivalent in the 2015-basis table and is not on this exam.)
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.