 The brushes, resembling paint rollers, are located on the front and back of the machine and help remove contaminating particles from the pool's floor, walls (and in some designs even the pool steps) depending on size and configuration.They also direct the particles into the internal filter bag.Saline chlorination units, electronic oxidation systems, ionization systems, microbe disinfection with ultra-violet lamp systems, and "Tri-Chlor Feeders" are other independent or auxiliary systems for swimming pool sanitation.