What is the minimum vertical air gap required where an indirect waste pipe discharges into a waste receptor, measured from the lowest point of the pipe to the flood-level rim of the receptor?
Not quite. The answer is B: 1 inch
Where the code calls for a drainage air gap, the vertical distance from the lowest point of the indirect waste pipe (or fixture outlet) to the flood-level rim of the receptor must be at least 1 inch. Do not confuse it with the water-supply air gap table, which scales with the faucet opening, or with the rule for potable water discharged to a drain, which is two pipe diameters but never under 1 inch. A trap on the receptor protects the drain side; it does nothing to stop the pipe itself from being submerged.
Reference: UPC 2021 §801.2 (Air gap or air break required)
Checked against the official text
Checked against the 2021 UPC text. Washington's exam is written against the 2015 edition, which we have not read for this section, so confirm it against your 2015 book.