A method and apparatus for conveying a cellulosic feedstock are disclosed. The apparatus, such as a holding tank, has a passage. At the outlet to the passage, a conveyance member is provided to convey the cellulosic feedstock laterally across the outlet. The conveyance member, e.g., at least one screw conveyor, may have a variable pitch along its length. The method comprises passing the cellulosic feedstock through an impregnation chamber to an outlet of the impregnation chamber; passing the cellulosic feedstock from the outlet of the impregnation chamber to an inlet of a holding tank; passing the cellulosic feedstock downwardly through the holding tank; maintaining a generally constant residence time in the holding tank; and subsequently subjecting the cellulosic feedstock to a hydrolysis process.