A filter vial and piston are provided where the vial has a cylindrical wall with a closed bottom and open top and with the hollow, tubular piston therein. The piston has a position stop located and configured to abut a mating position stop on the vial to limit relative movement of the piston and vial. The position stops are located to stop the distal end of the piston away from the bottom of the vial a distance of about 10-30% the height of the vial. That a material to be dissolved in a liquid in the vial and to remove unwanted molecules from the liquid with the piston forcing the liquid through the filter but not squeezing the slurry of material so as to force it into the filter.