Sewer mains shall be of adequate size and so designed in conjunction with related facilities to maintain a flow depth of not more than 0.9 times the internal diameter of said main at the periods of maximum flow. (Ord. 279 § 120, 1963).

Pressure conduits (inverted siphons) with the soffit depressed below the hydraulic grade line shall be permitted only where it can be shown that scouring velocities can be maintained over the wide range of flows subject to the approval of the county engineer. Under no conditions shall the velocity be less than three feet per second. Inverted siphons shall have not less than two barrels with a minimum pipe size of not less than six inches diameter. (Ord. 279 § 121, 1963).

All sewer mains shall be so designed to resist and withstand the maximum internal and external forces to which they may be subjected under normal operating conditions. (Ord. 279 § 122, 1963).

The minimum size for use in the sewer collection system shall be eight inches diameter. The use of a six-inch diameter main will be given consideration when all of the following conditions are met:
A. Where the design computations demonstrate that the connections thereto will be adequately served;
B. Where the velocity when flowing full will not be less than two feet per second;
C. Where the main dead ends and is not more than six hundred feet in length;
D. Where the manhole interval does not exceed three hundred feet; and
E. Where future extensions are not possible.
(Ord. 279 § 123, 1963).

In no case shall the diameter of a house connection be less than the house connection required by the county plumbing code. The minimum size house connection shall not be less than six inches diameter with the exception of single-family residences which shall not be less than four inches diameter. (Ord. 279 § 124, 1963).

Sewer mains shall be designed to maintain a minimum velocity of flow of two and one-half feet per second. A minimum velocity of two feet per second will be permitted in exceptional conditions when approved by the county engineer. (Ord. 279 § 125, 1963).

Sewer mains shall be designed such that the maximum velocity of flow shall not exceed ten feet per second. (Ord. 279 § 126, 1963).

Sewer mains shall be laid with uniform grade and alignment between manholes. (Ord. 279 § 127, 1963).

Manholes shall be installed at:
A. Every change of grade;
B. Every change of sewer main size;
C. Every change in alignment; and
D. At every junction of two or more sewer mains. The maximum interval between manholes shall be five hundred feet for mains less than eighteen inches diameter and six hundred feet for mains eighteen inches or larger diameter. Lamp holes shall not be substituted for manholes. (Ord. 279 § 128, 1963).

The horizontal separation between sewer and water mains shall be a minimum of five feet unless the soffit (top) of the sewer main is at least eighteen inches below the invert (bottom) of the water main. (Ord. 279 § 129, 1963).