In some embodiments, a medical-sample filtration device includes: a container including at least one wall forming an internal surface, a first aperture adjacent to a first end of the wall, and a second aperture adjacent to a second end of the wall; a movable insert positioned within the container and including an external surface of a size and shape to reversibly mate with the internal surface of the container; a positioning unit affixed to the internal surface close to the second aperture; a filter unit affixed to the second aperture; a sample conduit affixed to the filter unit; a valve unit attached to the sample conduit; and a connector operable to close the valve when the movable insert is in a predefined position relative to the container.