The invention relates to a decanter (2) for separating a supernatant arranged above a sludge in a settlement tank (1), wherein a withdrawal device (5, 16) with a receiving pipe (9, 18), which extends in the manner of a T-piece approximately perpendicular to a discharge pipe (4, 17), is attached to one end of the discharge pipe (4, 17). To reduce the production cost, it is proposed in accordance with the invention for the receiving pipe (9, 18) to be a polygonal pipe produced from sheet metal.