The design of combined sewer overflow (CSO) chambers is of critical importance to the effective retention of pollutants and solids within the sewer system and such that the impact of aesthetic pollution to water courses and bathing beaches is minimized. Recommended designs of CSO chamber include high side weir chambers, stilling ponds and dynamic separators in the form of the vortex chamber with peripheral spill weir and the Stormking(R) hydrodynamic separator. This paper describes a performance evaluation of the last two types of chamber, carried out within the Water Engineering Laboratory at the University of Sheffield using a range of full-scale particulate-condoms, sanitary towels, release tapes and cotton bud sticks-for a range of hydraulic conditions.