Abstract: An apparatus and method of cleaning a diffraction grating with minimal use of cleaning chemicals. The apparatus includes a processing vessel having a sump at a lower end thereof, and an inclined platform for receiving a diffraction grating within the processing vessel so that a top surface of the diffraction grating is in an inclined position. This enables fluid runoff from the top surface of the diffraction grating to drain into the sump where it is recirculated via a recirculation line which channels (using a pump) fluid from the sump to a recirculation spout positioned to direct fluid onto the top surface of the diffraction grating. Additionally, by measuring the amount of waste cleaning fluid (acid) collected, a neutralizing agent may be dispensed to neutralize any remaining cleaning fluid in the system so that waste fluid may be released without limitation.