Abstract: A method is provided for testing for presence of a particulate selected from the group consisting of: a microorganism, a fungus, a bacteria, a spore, a virus, a mite, a biological cell, a biological antigen, a protein, a protein antigen, and a carbohydrate antigen. The method includes (a) collecting, in a tube (22), fluid that potentially contains the particulate, (b) using a plunger (24) to push the fluid through a filter (26) disposed at a distal portion of the tube or at a distal end of the plunger, and subsequently, (c) while the filter is inside the tube, ascertaining if any of the particulate was trapped by the filter by applying a particulate-presence-testing-facilitation solution to the filter. Other embodiments are also described.