Abstract: Apparatus and method is disclosed for washing out the interiors of truck and trailer bodies. A washer head is carried on an elongate boom which is mounted on a pedestal for traversing movement along a horizontal axis. The boom is moved by means of a drive motor which is in engagement with a chain having its opposite ends secured to opposite ends of the boom. The washer head includes a frame which is mounted on an end of the boom for pivotal movement between elevated and lower positions. The frame is constructed in a four-bar linkage arrangement for movement through a lateral angle to accommodate any misalignment as the boom enters the trailer. A cam engages a hoist arm connected with the frame of the washer head, and a motor is controlled to rotate the cam for raising and lowering the washer head. The washer head mounts a brush which is operated as the boom withdraws from the trailer interior.