To promote student involvement in the reduction of chemical waste generated by teaching laboratories, a method published by Flinn Scientific for the treatment of waste sodium molybdate has been modified for use in treating waste generated by the popular molybdenum blue method for the analysis of phosphate in natural water samples. In this teaching laboratory, students convert molybdenum-containing anions in their phosphate lab waste to the corresponding insoluble calcium salts for disposal of the precipitate in the trash and disposal of the filtrate down the drain. Determination of a percent yield is offered as an additional experiment. Considerable evidence is presented that this revised method for waste treatment decreases molybdenum levels in the filtrate to levels well below stated limits for sink/sewer disposal.