As stormwater runoff flows over impervious surfaces, it suspends and transports various pollutants from their original locations and often conveys them into municipal separate storm sewer systems (MS4s). Most municipalities and state highway agencies in the United States have developed stormwater management guidelines to ensure compliance with the EPA’s MS4 standards, including allowable methods and practices to remove pollutants from stormwater influent flowing into MS4s. Catch basin inserts (CBIs) have become an increasingly popular option for pollutant removal from stormwater. However, limited data are available to ensure that these practices meet required treatment standards. This study details the design, construction, calibration, and validation of an apparatus for full-scale testing of CBIs. CBI testing is designed to evaluate total suspended solids (TSS) removal efficiency reduction at three flow rates, 1.7, 3.4, and 5.1  L/s (0.06, 0.12, and 0.18  ft3/s), at an influent concentration of 450  mg/L (0.028  lb/ft3). Testing of a nonproprietary CBI revealed that the device removed 62.1%, 65.1%, and 51.7% of sediment introduced and reduced average TSS by 57%, 53%, and 49% over flow rates tested, respectively.