This paper is concerned with a major intercepting sewer currently being tunnelled between 50 and 100 ft (15 and 30 m) below the streets of mid Metropolitan Toronto. The sewer is 43 210 ft (13.17 km) long, varies from 5–10 ft (1.5–3.0 m) in diameter and will serve an area of 9466 acres (3834 ha). Flows in the sewer will be remotely controlled by sluice gates and level sensing devices. Vortex structures are used to transfer flow from street level to the tunnelled sewer. The paper describes the conception, design, and construction of the interceptor system.