Section 31. All traps must be well supported, and set true with respect to their water levels. The size for traps must not be less than those given in the following:
Traps for water-closets, four inches in diameter.
Traps for slop-sinks, one and one-half inches to three inches in diameter.
Traps for kitchen sinks, one and one-half inches in diameter.
Traps for wash-trays, two inches in diameter.
Traps for (bowl) urinals, one and one-half inches in diameter.
Traps for washstands, one and one-fourth inches in diameter. All bath-tubs shall be supplied with drumtrap, not less than three inches in diameter, with three-inch trap-screws on floor line. In case where an additional fixture is required in a building, and it is impossible to get re-vent pipes for the trap, the Board or Bureau of Health shall designate the kind of trap to be used. This shall not be construed to allow traps without re-vents in new buildings.