Episode 1

The first episode follows the creation of the first stretch of the supersewer in east London. Lead engineer Emmanuel Costes has to build a massive 80-metre deep shaft that connects to the supersewer and make it watertight using a specialist technique called 'slipform'. It is a risky approach as it involves pouring concrete constantly for 15 days - and delays could spell financial disaster. The programme follows Steve Perry and his team at the treatment works in Beckton as they attempt to install the biggest pumps ever used in Britain to deal with sewage. The pumps are critical - with so much more sewage due to head to Beckton via the new supersewer, each one has to be capable of pumping three cubic metres of sewage per second. If they aren't installed correctly, millions of tonnes of the capital's waste will be stuck underground. Originally built when the population was two million, the Victorian sewers now service nearly nine million Londoners. The episode shows how this growing population means the existing sewers need constant maintenance in order to work at full capacity. With huge residential developments being built across the city, a group of sewer technicians (aka flushers) are sent in to survey the old sewers and plan for new connections. The programme follows Emmanuel, Steve and the team, who are up against the clock to finish the first section of the new supersewer so that it can be put to work in time for the opening ceremony.