Abstract: In a method for keeping outfall drainage in service whilst constructing sewerage, wherein a main drain is laid in the position of an old drain or in a new line by pipe or shield tunnelling under closed or semi-open construction using a working pipe or shield (1) at the tunnelling end (9), at essentially the same time as the working pipe or shield (1) is tunnelling, at least one outfall drain (30) is laid below ground through at least one working orifice (20) in the working pipe or shield (1), so that the outfall drain (30) lies alongside the main drain. A device suitable for implementing the method has a working pipe or a shield (1) with at least one working orifice (20) for laying at least one underground outfall drain (30) alongside the main drain from the interior of the working pipe or shield (1).