A device for preparing biological samples including a fixed support of which the base extends in a first plane, a filtration block that can be removable, the filtration block including a collecting tank that itself includes a filtering device extending in a second plane and dividing the collecting tank into a collection area and a suction area, the suction area being designed to be connected to a suction device, the second plane of the filtering device being inclined relative to the plane of the base of the fixed support.