Theory:

Sewage
The wastewater that is released by the homes, offices, Industries, hospitals and various other sources is known as sewage.
As the rainwater flowing into the drains during heavy rains contains pollutants that it washes off from the roads and rooftop, it is also considered as sewage. Any liquid waste with impurities and pollutants is sewage.
Sewage is a complex mixture of suspended solids and various impurities such as organic and inorganic impurities, nutrients, saprophytes and disease-causing bacteria and other microbes. All these impurities are in general known as contaminants.
Given below are the various impurities and their examples:
 
Impurity
Example
Organic impurities
Human faeces, animal waste, oil, urea (urine), pesticides,
herbicides, fruit
and vegetable
wastes.
Inorganic impurities
Nitrates, Phosphates,
metals.
Nutrients
Phosphorus and Nitrogen.
Bacteria
– Such as Vibrio cholera which
causes cholera
and Salmonella paratyphi which
causes typhoid.
Other microbes
Such as protozones which cause dysentery.
 
Sewers and sewerage
The large and small pipes which carry sewage water are known as sewers.
The network consisting of these sewers is known as Sewerage.
The sewerage is a transport system that carries the sewage water from  the point where it is produced to the point where it is disposed.
 
The point where the sewage is disposed is known as the treatment plant.
The sewerage consists of manholes at every 50m to 60m. These manholes are installed at a the junctions where two or more sewers intersect or change their directions.