Abstract: The invention relates to a device (1) for the separation of air out of a waste water mixture, in particular such a waste water mixture as arises at a medical or dental-medical treatment station, having a housing (2) which has a round cross-sectional form in horizontal cross-section, an inlet (3) for the waste water mixture which tangentially opens into the housing (2), a first outlet (4) for air, arranged above the inlet (3), and a second outlet (5) for heavy materials, such as waste water, arranged below the inlet (3). For the purpose of improving the separation function, the inlet (3) is arranged in the region of a hollow cone shaped peripheral wall section (6) of the housing (2), which section is downwardly divergent.