Lavatory for connection to a composting container (1) or a sewage pipe forming part of a sewage system. The lavatory has a seat part (11), a lid (12) adapted to the seat part, and a hollow support body (13) supporting the seat part. The support body (13) surrounds or forms an inner duct through which fecal matter passes to the container or the sewage pipe. The rear wall of the duct slopes backwards from the seat part (11) in the downward direction so that it forms an angle (alpha) with the vertical.