An additive-manufacturing build-material container comprises a reservoir to hold build material, a build-material outlet structure to allow build material to exit the reservoir through an outlet opening in a top portion of the reservoir, a longitudinal collection unit (313a) to collect build material from the bottom and guide the build material to the outlet opening at the top, and bottom-venting structure to admit vent gas into a bottom portion of the reservoir. The bottom-venting structure may include a vent tube to admit venting gas into the bottom portion of the reservoir. A concentric collection tube structure may be employed including the longitudinal collection tube nested within a vent tube (333A, 354A). The concentric collection tube structure may be mounted along the central axis of the reservoir.