Abstract: This invention relates to the combination of an aeration system and flexible diffuser assembly, especially for use in a sewage treatment tank, where the system includes a plurality of fluid medium transmission conduits, with each conduit provided with at least one flange projecting therefrom, where the flange includes a base plate mounted thereto and a central opening communicating with said conduit. The diffuser assembly comprises a first member having a flat continuous annular face portion and a central recess with a bore aligned with the central opening. A locking bolt member is provided to threadably engage the bore and central opening, where the bolt member includes a central, through orifice communicating with the conduit through which the fluid medium may pass.