Sec. 492. Traps to fixtures.
The traps of all fixtures, except otherwise specified, must be
protected from syphonage and their waste ventilated by special
line of iron vent pipe not less than two inches inside diameter.
The short branches from these lines to each trap shall be two
inches inside diameter for three and four inch traps and one and
one-half inches inside diameter for smaller trap. No trap of any
kind to be smaller than one and one-half inches inside diameter
for any fixture. Branch vents from all traps must be connected
above the outlet of any and all fixtures in the group in such a
manner as to prevent the waste water flowing through the vent
pipes should the waste or soil pipes become obstructed. Four-inch
drum traps, with suitable covers above floor, to be used under
all bathtubs except as otherwise specified.
