is carried to the treatment plant via sanitary
sewers. The connection from the house to the sewer system
is a pipe, about 6” in diameter. A larger pipe (8-12” in diameter),
called a collecting sewer,
runs down the street picking up the wastewater from individual sewers.
These pipes eventually run to an interceptor
sewer which delivers the flow to the treatment plant. In
large cities, interceptor sewers can be huge, sometimes big enough
to drive a car through! Engineers design sewer systems to take advantage
of gravity flow, but sometimes pumping is required.
is collected by storm drains and flow through storm sewers to settling
ponds or lakes and rivers.