The RetroFAST or RetroFITT-ee (energy-efficient version) unit from Bio-Microbics is designed as a simple upgrade to enhance a conventional septic system or renovate a biologically failed septic system. It installs directly in the existing tank to create an optimized treatment environment using submerged, fixed-film media for microbial growth with an energy-efficient aeration system. It constantly sends effluent rich in dissolved oxygen to the drainfield. Where sites and regulations allow, it can be used in new installations. It is designed to immediately deliver high levels of treatment to help prevent formation of clogging layers. 800/753-3278; www.biomicrobics.com.