Abstract: A submicron size particle filter is mounted within a hot water vacuum extraction machine beneath a vertical riser tube which extends upwardly from an outer casing bottom wall. The riser tube is subject to vacuum pressure to remove contaminant and liquid free air from a recovery tank. An air filter chamber open to the lower end of the riser tube carries the secondary filter holder assembly consisting of a perforate secondary filter holder about an open pore filter element to filter out contaminants of submicron size. The secondary filter holder is formed of an open frame circular base member with a filter disk retaining ring snap fitted thereto and sandwiching the open pore filter element.