The Clarifier Research Technical Committee’s draft protocol for evaluating final settling tank performance was field applied at New York City’s Rockaway Water Pollution Control Plant. The test tank was a rectangular unit 76.2 m (250 ft) long by 17.2 m (56.5 ft) wide with an average depth of 3.7 m (12 ft). The test tank consisted of three equally sized bays separated by knee walls approximately 1 m (3.3 ft) high. Sludge withdrawal was from a hopper located at mid-tank. Sludge collection flights upstream of the sludge hopper moved co-currently with respect to the flow through the tank. Conversely, sludge collection flights downstream of the sludge hopper moved counter-currently with respect to the flow through the tank.