(2) To the maximum extent practicable, sewers are laid in straight lines
(see Figures 1-4, 1-5). Corners and sharp bends slow the flow rate, permit clogging,
and make line cleaning difficult. Manholes (see Figure 1-6) are located at each change
of slope of a branch or larger sewer and generally are placed at the end of each lateral.
Where sewers connect, a Y-channel is formed in the base of the manhole.
Figure 1-5. Good and bad plans for sewer lines.
(3) Care must be exercised in the installation of a wastewater collection
system to prevent the occurrence of indirect cross connections.
(a) Indirect cross connections can occur when sewer lines and
potable-water lines are laid underground in the same trench. The cross connection
occurs when the water line breaks and admits wastewater that has escaped through
loose joints or breaks in the sewer lines. Avoid laying these lines in the same trench.
The water piping is to be enclosed in a separate trench above the sewer line.
(b) Indirect cross connections can also occur when sewer and water
lines are laid separately but nearby especially in acid soils or land areas made from
cinders. A method for avoiding such cross connections is shown in Figure 1-7.