Abstract: The specification discloses an apparatus for washing the interior of an elongate, generally rectangular freight container. The apparatus includes a wash dolly and a transfer carriage adapted to carry the wash dolly into alignment with the open end of the container. A control system including electrical and hydraulic circuits causes the wash dolly to travel off of the transfer carriage, along substantially the entire length of the container, and back onto the transfer carriage. The wash dolly scrubs and sprays the interior of the container as it travels.