Fuller learned from his Louisville work when he designed the investigations at Cincinnati, Ohio for the purification of Ohio River water. From 1897 to 1899, Fuller investigated mechanical filtration using the addition of aluminum sulfate followed by a sedimentation step before the final filtration process. After completing the Cincinnati filtration report, Fuller opened a single person consulting practice in New York City. One of his first assignments was from the East Jersey Water Company to design a 30 million gallon per day mechanical filtration plant at Little Falls, New Jersey. The plant was a milestone in public health protection because it incorporated all of Fuller's findings from his research over the previous 10 years and it became the model for the design of subsequent drinking water filtration facilities. On June 19, 1908, Fuller was hired by John L. Leal to design and build a chlorination system for the Jersey City, New Jersey water supply at Boonton Reservoir on the Rockaway River. Given an impossible deadline as a result of a New Jersey Chancery Court order, Fuller successfully completed the chlorination system in 99 days. John L. Leal developed the basic concept of applying chlorine in the form of a dilute solution of chloride of lime (calcium hypochlorite) at fractions of a ppm. Fuller modeled his chloride of lime feed system on the aluminum sulfate feed system that he designed for the Little Falls Water Treatment Plant. The chlorination facility fed 0.2 to 0.35 ppm of chlorine to an average water flow of 40 million gallons per day from Boonton Reservoir. Fuller testified as an expert witness for the defendants, the Jersey City Water Supply Company, in both trials that resulted from a lawsuit filed by Jersey City against the water company. The chlorination system that he designed and built was declared a success by the Special Master, William J. Magie, and was judged capable of supplying Jersey City with water that was "pure and wholesome." The success of the Boonton chlorination system was due, in no small part, to the engineering excellence of Fuller. Chlorine use exploded after the positive ruling by Justice Magie and typhoid fever and other waterborne diseases were conquered as a direct result of Fuller's reliable engineering of the first chlorination system. The foundation of Fuller's expertise in sewage treatment was laid at the Lawrence Experiment Station in Massachusetts. He later went on to design and supervise the construction of some of the most important sewage treatment plants in the U.S. Fuller and his partner Rudolph Hering were responsible for the design of the earliest Imhoff tank sewage treatment facilities in the U.S., which were located in Chatham, New Jersey and Atlanta, Georgia.