A buffer box for use in a vacuum drainage system. The buffer box defines a reservoir of known effective size which provides substantially consistently sized slugs of liquid which may be efficiently pulled up a vertical lift. The buffer box includes an outlet and an air intake orifice which may be sized relative to one another so that only liquid from the reservoir is evacuated. The outlet has an upper edge which may be spaced from a base portion of the buffer box at a height which optimizes liquid velocity out of the box and defines a level above which only water is evacuated from the reservoir.