Design procedure for sanitary sewers
How to Design Sanitary Sewer
Design flow:

Calculate the average wastewater flow, Qavg = (7080) % of average water consumption.

Select a peak factor, PF = [(18+√P)/(4+√P)], where P = population in thousands.

Calculate the peak wastewater flow, Qpeak = (PF * Qavg)

Calculate the allowance for industrial and commercial sewage at the rate of 3734 m^{3}/km2/d (Qind)

Calculate the infiltration allowance, Qinf = (510) % of Qavg

Find the design discharge by adding peak flow, industrial and commercial allowance and infiltration allowance, i.e., Qdesign = Qpeak + Qind + Qinf
Diameter of the sewer:
Assume a suitable value for cleaning velocity, determine the area (diameter) of the sewer by using the relation, Area, A = (Qdesign/V)
Slope using Manning’s equation determine the slope of sewer, V = [(1/n) *(R2/3)*(√S)]