In every case where a plumbing outlet or plumbing
fixture is installed or located below the elevation of the curb or
property line, an approved type of backwater trap or an approved type
of backwater sewer valve shall be installed between the outlet and
the public sewer in such a manner as to prevent sewage from flowing
back or backing up into any such outlet or plumbing fixture. Every
such trap or valve shall be installed in the basement in a box or
manhole of concrete, cast iron or other material approved by the Building
Inspector so that it will be readily accessible at all times. The
trap or valve shall be placed only in the drain line serving the fixtures
that are located below the elevation of the above-mentioned curb or
property line, and no drainage from fixtures located above this elevation
shall pass through such trap or valve.
Whenever it shall come to the attention of the Engineer that sewage is overflowing from any plumbing fixture which is below the grade of the manhole in the street or right-of-way due to the backing up of sewage in the public sewer, or due to the pressure in the public sewer or due to any cause whatsoever, except a temporary stoppage in any such plumbing fixture, said Engineer may order and require such plumbing fixture to be plugged up or capped or may require that a backwater trap or backwater sewer valve, required by §
241-15, be installed to prevent such overflow.