At which point must a drain be disconnected when it is no longer required?

The drain must be disconnected at the junction with the live drain because this location provides a clear and effective point for separation. Disconnection at this point ensures that there is no possibility of backflow or blockage in the existing drainage system. It allows for proper sealing and prevents any potential infiltration of wastewater from the disconnected section into the active drain. This practice is crucial for maintaining the integrity and functionality of the overall drainage system.

In contrast, disconnecting at other points, such as the backfill line or the highest point of the drain, might not provide the same level of certainty in terms of preventing contamination or ensuring proper drainage. Disconnecting at the inspection chamber could complicate access and maintenance of the drainage system. Hence, the junction with the live drain is the most appropriate choice for a safe and effective disconnection.