A breather-sampling-filler assembly (10) for liquid lubrication systems is provided which includes a primary unit (block) (14) adapted for permanent or semi-permanent attachment to a wall (12) of a lubrication system in covering relationship to a lubrication system access opening (13). The unit (14) includes individual breather, fill, and sampling ports (16, 18, 20), and is designed to support a breather (22) in communication with breather port (16), a fill assembly (24) in communication with fill port (18), and a sampling assembly (26) in communication with sampling port (20). The breather (22) includes at least one vent opening (60) and had a selected media (62) therein for desired treatment of solid and liquid airborne contaminants passing into and out of the lubrication system. Use of the assembly (10) permits continuous treatment of air entering and leaving the lubrication system (12), and also allows quick, trouble-free liquid filling and sampling while avoiding introduction of contaminants into the lubrication system liquid and air pollution from the lubrication system (12)