A flexible, inline filter/dryer for installation in an air/gas line delivering compressed air or gas to an air/gas-driven tool. The filter/dryer includes a first end connector, a second end connector, and a flexible main body extending between the first and second end connectors. A drying composition, such as desiccant beads, substantially fills the main body and is retained therein by a retaining system that can include one or more filter elements and a plenum-defining spacer element.