An additive-manufacturing build-material container (201) comprises a reservoir to hold build material, an outlet opening in a top portion of the reservoir, an outlet tube structure including a longitudinal collection unit to collect build material from the bottom and guide the build material to the outlet opening at the top, upon application of a suction force at the other end thereof, and to guide the collected build material to the outlet opening at the top; and a vent opening in a top portion of the reservoir to admit gas from outside the reservoir into the reservoir to follow a gas flow path through the vent opening, through the reservoir and into the one end of the longitudinal collection tube; wherein on the gas flow path there is at least one turbulent gas-flow-generation feature (237) to generate turbulent gas flow in a region that is within the reservoir and outside the longitudinal collection tube.