24 CFR § 3280.606 - Traps and cleanouts.
(a) Traps -
(2) Combination Fixtures. For the purposes of drainage and ventilation requirements, a two- or three-compartment sink, up to three single sinks, or up to three lavatories may be connected to one “P” trap and considered as a single fixture, so long as the sinks and lavatories are in the same room, have waste outlets not more than 30 inches apart, and have flood level rims at the same level. The “P” trap must be installed at the center fixture when three such fixtures are installed.
(3) Prohibited traps. A trap which depends for its seal upon concealed interior partitions shall not be used. Full “S” traps, bell traps, drum traps, crown-vented traps, and running traps are prohibited. Fixtures shall not be double- trapped.
(4) Material and design. Each trap shall be self-cleaning with a smooth and uniform interior waterway. Traps shall be manufactured of cast iron, cast brass, or drawn brass tubing of not less than No. 20 Brown and Sharpe gage, or approved or listed plastic, or other approved or listed material. Union joints for a trap shall be beaded to provide a shoulder for the union nut. Each trap shall have the manufacturer's name stamped or cast in the body of the trap, and each tubing trap shall show the gage of the tubing.
(5) Trap seal. Each “P” trap shall have a water seal of not less than 2 inches and not more than 4 inches and shall be set true to its seal.
(7) Location. Each trap shall be located as close to its vent and to its fixture outlet as structural conditions will permit.
(8) Length of tailpiece. The vertical distance from a trap to the fixture outlet shall not exceed 24 inches.
(i) Grade of trap arm. The piping between a “P” trap and the fixture tee or the vented waste line shall be graded 1/4 inch per foot towards the vent and in no event shall have a slope greater than its diameter. The vent opening at fixture tees shall not be below the weir of the “P” trap outlet.
(ii) Trap arm offset. The piping between the “P” trap and vent may change direction or be offset horizontally with the equivalent of no more than 180 degrees total change in direction with a maximum of 90 degrees by any one fitting.
(iv) Removability of traps, etc. Traps shall be designed and installed so the “U” bend is removable without removing the strainers from the fixture. Continuous waste and tail pieces which are permanently attached to the “U” bend shall also be removable without removing the strainer from the fixture.
(b) Cleanout openings -
(1) Location of cleanout fittings.
(i) Cleanouts shall be installed if the drainage system cannot be cleaned through fixtures, drains, or vents. Cleanouts shall also be provided when fittings of more than 45 degrees are used to affect an offset except where long turn ells are used which provide sufficient “sweep” for cleaning.
(iii) A cleaning tool shall not be required to pass through more than 360 degrees of fittings, excluding removable “P” traps, to reach any part of the drainage system. Water closets may be removed for drainage system access.
(2) Access to cleanouts. Cleanouts shall be accessible through an unobstructed minimum clearance of 12 inches directly in front of the opening. Each cleanout fitting shall open in a direction opposite to the flow or at right angles to the pipe. Concealed cleanouts that are not provided with access covers shall be extended to a point above the floor or outside of the manufactured home, with pipe and fittings installed, as required, for drainage piping without sags and pockets.
(3) Material. Plugs and caps shall be brass or approved or listed plastic, with screw pipe threads.
(4) Design. Cleanout plugs shall have raised heads except that plugs at floor level shall have counter-sunk slots.