Radiator repair shops most commonly use hot caustic solutions to clean radiator sections prior to resoldering. The hot caustic, or 'boil-out' solutions as they are called in the trade, become contaminated with dirt, rust flakes, paint flakes and miscellaneous particulate debris. In addition, the 'boil-out' solutions dissolve lead, copper, zinc, and tin from the brass radiator components and the solder used for assembly. A portion of the dissolved heavy metals are in true solution whereas an important percentage precipitates as metal hydroxide, 'quasi-colloids'. Cooling the solutions and allowing the dissolved metals to precipitate and settle enables the operator to recycle up to 80 percent of the solution. Preliminary test work has shown that sodium sulfide added to the caustic 'enhanced sludge' solution will precipitate the metal hydroxides. The precipitates are coarse enough to settle out of the solution and leave a stripped, clarified liquid. This means that it should be feasible to design a precipitation and clarification system that could be used by any small radiator repair shop and eliminate this hazardous waste stream from the environment. The work was performed between May 15, 1987, and June 30, 1988, at the University of Minnesota, Duluth.