A filter device for separating a liquid mixture, whereby the filter device comprises a vessel which is configured to contain at least one first filter element, whereby the vessel comprises an entry port for introducing the liquid mixture into the first filter element, whereby the vessel further comprises a flat vessel base surface configured to allow the vessel to stably stand on a horizontal flat ground surface when the vessel base surface is parallel to and level with the horizontal flat ground surface, whereby the vessel further comprises a vessel mantle surface extending from a periphery of the vessel base surface in a direction opposite to the vessel base surface, whereby the filter device comprises at least one housing (3, 3a, 3b) which is configured to contain at least one second filter element, whereby the housing (3, 3a, 3b) comprises a flat housing base surface configured to allow the housing to stably stand on a horizontal flat ground surface when the housing base surface is parallel to and level with the horizontal flat ground surface, whereby the housing (3, 3a, 3b) further comprises a housing mantle surface extending from a periphery of the housing base surface in a direction opposite to the housing base surface, whereby the vessel mantle surface comprises a re-entrant section forming a recess configured to accommodate the housing (3, 3a, 3b), whereby a mating side of the housing mantle surface is configured to fit into the recess formed by the re-entrant section, whereby the re-entrant section and the mating side are provided with connection means to fluidly connect an outlet of the first filter element with an inlet of the second filter element in a detachable way when the mating side of the housing mantle surface is fitted into the recess formed by the re-entrant section, characterised in that the re-entrant section is extending from the vessel base surface, and that 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 such that the outlet of the first filter element is fluidly connected with the inlet of the second filter element. whereby the vessel comprises an entry port for introducing the liquid mixture into the first filter element, whereby the vessel further comprises a flat vessel base surface configured to allow the vessel to stably stand on a horizontal flat ground surface when the vessel base surface is parallel to and level with the horizontal flat ground surface, whereby the vessel further comprises a vessel mantle surface extending from a periphery of the vessel base surface in a direction opposite to the vessel base surface, whereby the filter device comprises at least one housing (3, 3a, 3b) which is configured to contain at least one second filter element, whereby the housing (3, 3a, 3b) comprises a flat housing base surface configured to allow the housing to stably stand on a horizontal flat ground surface when the housing base surface is parallel to and level with the horizontal flat ground surface, whereby the housing (3, 3a, 3b) further comprises a housing mantle surface extending from a periphery of the housing base surface in a direction opposite to the housing base surface, whereby the vessel mantle surface comprises a re-entrant section forming a recess configured to accommodate the housing (3, 3a, 3b), whereby a mating side of the housing mantle surface is configured to fit into the recess formed by the re-entrant section, whereby the re-entrant section and the mating side are provided with connection means to fluidly connect an outlet of the first filter element with an inlet of the second filter element in a detachable way when the mating side of the housing mantle surface is fitted into the recess formed by the re-entrant section, characterised in that the re-entrant section is extending from the vessel base surface, and that 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 such that the outlet of the first filter element is fluidly connected with the inlet of the second filter element.