Abstract: Apparatus is disclosed for use in the manufacture of rod like elements, for example cigarette filters formed of filamentary tow, for dissipating conveying gas from a conduit through which the tow is conveyed pneumatically through a series of processing stations. To effectively dissipate the gas from the conduit, the invention provides axially spaced rings of gas dissipation ports in the conduit. The ports in the upstream rings are inclined rearwardly to provide gas dissipation in a direction which is counter-current the direction of travel of the tow through the conduit. The ports in adjacent rings are offset circumferentially so as to improve the distribution of ports around the circumference of the conduit in the section used for gas dissipation.