Self cleaning velocity:

When there is no solids get deposited in the invert of the sewer of minimum velocity , then minimum velocity is termed as self cleaning velocity

Size of sewers:

1. The minimum size of public sewer should not be less than 0.15m. But in actual practice it is recommended as 0.2m.

2. Maximum slopes are available in hilly areas where size of sewer may be 0.1m.

3. Generally the sewers 0.1 m diameter are permitted up to a maximum length of 6m or so if a sewer length line is more than 6m then diameter of 0.15m is not allowed.