Abstract: A filter device for separating a liquid mixture, including a vessel with first filter element. The vessel comprises a flat vessel base surface and vessel mantle surface. , including a housing with a second filter element. The housing comprises flat housing base surface and housing mantle surface. The vessel mantle surface comprises re-entrant section forming recess. A mating side of the housing mantle surface is configured to fit into the recess, whereby the re-entrant section and the mating side are provided with connection means to fluidly connect the first filter element with the second filter element. The re-entrant section extends from the vessel base surface, and the vessel base surface and the housing base surface are parallel and level in the same plane when the mating side of the housing mantle surface is fitted into the recess formed by the re-entrant section.