A method comprising: applying pressure to drive liquid contained in a liquid container (30, 930, 1430) of a testing device (20, 120, 290, 320, 420, 520, 620, 820, 920, 1420, 1520, 1620, 1720) through a filter (32, 132) of the testing device, wherein the filter (32, 132) is disposed in or downstream of the liquid container (30, 930, 1430), and wherein the liquid includes at least one substance selected from the group of substances consisting of gargled fluid, saliva not swabbed from a throat of a patient, and an incubated culture medium containing a biological sample; and thereafter, testing for the presence of particulate trapped by the filter (32, 132) while the filter (32, 132) is disposed in the testing device, characterized in that: applying the pressure comprises applying the pressure to drive the liquid contained in the liquid container (30, 930, 1430) (a) through the filter (32, 132) and (b) then through one or more valves (50, 60, 960, 1460, 1560, 1660, 1760) of the testing device (20, 120, 290, 320, 420, 520, 620, 820, 920, 1420, 1520, 1620, 1720), wherein the one or more valves are disposed downstream of the filter (32, 132), and testing comprises testing, within the testing device, for the presence of particulate trapped by the filter (32, 132) by applying an extraction reagent to the filter (32, 132) while the filter (32, 132) is disposed in the testing device and the one or more valves are closed so that the extraction reagent is retained by the filter (32, 132) rather than passing through the filter (32, 132), such that the extraction reagent bathes the filter (32, 132). applying pressure to drive liquid contained in a liquid container (30, 930, 1430) of a testing device (20, 120, 290, 320, 420, 520, 620, 820, 920, 1420, 1520, 1620, 1720) through a filter (32, 132) of the testing device, wherein the filter (32, 132) is disposed in or downstream of the liquid container (30, 930, 1430), and wherein the liquid includes at least one substance selected from the group of substances consisting of gargled fluid, saliva not swabbed from a throat of a patient, and an incubated culture medium containing a biological sample; and thereafter, testing for the presence of particulate trapped by the filter (32, 132) while the filter (32, 132) is disposed in the testing device, characterized in that: applying the pressure comprises applying the pressure to drive the liquid contained in the liquid container (30, 930, 1430) (a) through the filter (32, 132) and (b) then through one or more valves (50, 60, 960, 1460, 1560, 1660, 1760) of the testing device (20, 120, 290, 320, 420, 520, 620, 820, 920, 1420, 1520, 1620, 1720), wherein the one or more valves are disposed downstream of the filter (32, 132), and testing comprises testing, within the testing device, for the presence of particulate trapped by the filter (32, 132) by applying an extraction reagent to the filter (32, 132) while the filter (32, 132) is disposed in the testing device and the one or more valves are closed so that the extraction reagent is retained by the filter (32, 132) rather than passing through the filter (32, 132), such that the extraction reagent bathes the filter (32, 132). applying the pressure comprises applying the pressure to drive the liquid contained in the liquid container (30, 930, 1430) (a) through the filter (32, 132) and (b) then through one or more valves (50, 60, 960, 1460, 1560, 1660, 1760) of the testing device (20, 120, 290, 320, 420, 520, 620, 820, 920, 1420, 1520, 1620, 1720), wherein the one or more valves are disposed downstream of the filter (32, 132), and testing comprises testing, within the testing device, for the presence of particulate trapped by the filter (32, 132) by applying an extraction reagent to the filter (32, 132) while the filter (32, 132) is disposed in the testing device and the one or more valves are closed so that the extraction reagent is retained by the filter (32, 132) rather than passing through the filter (32, 132), such that the extraction reagent bathes the filter (32, 132).