Pick up the correct statement from the following:

Answer: Option D

Key Points:

1. Maximum daily flow = 2 times the average daily flow:
This is a standard assumption used in wastewater engineering to account for peak flow conditions.

2. Maximum daily flow = (2/3) × average daily flow:
This is another consideration often used in specific design scenarios, depending on regional practices and flow characteristics.

3. Sewers are designed for minimum permissible velocity at minimum flow:
To prevent sediment deposition, sewers are designed to maintain a minimum velocity, even during low-flow conditions.
This ensures the self-cleansing capability of the sewer system.

Therefore: All the statements are correct, making the correct answer Option D: All the above.