Abstract: An apparatus for washing or otherwise treating parts includes a modular support structure for a conveyor from which the parts are suspended and further includes transparent walls that enable visual observation of the treatment process. The support structure includes a plurality of upstanding, longitudinally spaced apart stanchions, each of which has a top piece adapted to engage the uppermost end of a flexible sheet of transparent material such as vinyl. In one embodiment, the lowermost end of each sheet of material is immersed in water contained within an elongate trough that extends along both sides of the apparatus. Thus, a vapor seal is formed that prevents vapors and chemicals from escaping the interior of the apparatus. Dams are placed in the trough at longitudinally spaced intervals to prevent mixing of the chemicals that are collected in the trough. Additional embodiments require no troughs, and include metallic panels that replace or overlie one or more of the vinyl sheets.