Discrete interval sampling tools. Compare sampling through probe rods using an expendable point (left), sampling through probe rods using a retractable point (center), and sampling through inner tubing using a post-run tubing (PRT) system (right). The PRT system is a downhole sampling system. After the point is advanced, the tubing is attached, downhole, to an adapter at the top of the sampling chamber. Courtesy of Geoprobe Systems.