Septic tank
A septic tank is an underground chamber made of concrete, fiberglass or plastic through which domestic wastewater (sewage) flows for basic treatment. Settling and anaerobic processes reduce solids and organics, but the treatment efficiency is only moderate (referred to as "primary treatment"). Septic tank systems are a type of simple onsite sewage facility (OSSF). They can be used in areas that are not connected to a sewerage system, such as rural areas. The treated liquid effluent is commonly disposed in a septic drain field which provides further treatment. However, groundwater pollution may occur and can be a problem.
Submarine escape training facility
The Submarine Escape Training Tank (SETT) is a deep facility primarily operated to conduct training with submarine escape equipment, operated by the Royal Navy. 
The facility, located at Fort Blockhouse, Gosport opposite HMNB Portsmouth, includes a fresh, chlorinated water column with a single escape chamber (as fitted to some classes of RN submarines) mounted at the base, through which students can conduct a fully representative escape cycle from , closely replicating actions which would be required if forced to abandon a distressed submarine from depth. The SETT has its own dedicated boiler house to maintain its water temperature at 34 °C (94 °F). The SETT was commissioned in 1954, with the first students trained in July of that year. Since that time completion of ‘the Tank’ has been a rite of passage for all RN Submariners. Training includes ascents from increasing depths as a major element, but in addition is underpinned by lectures and practical training in how to survive within a disabled submarine, operation of emergency equipment and survival techniques on reaching the surface – a package of potentially life saving skills. Over the years, the SETT has been used to train submariners from Italy, USA, Greece, Canada, Israel, Russia, Venezuela, Turkey, Australia and the Netherlands – with the staff and facility enjoying a worldwide reputation for excellence and good practice. Owing to a combination of increased safety associated with modern submarine design, submarines operating in areas where escape would be impossible with current equipment and the risk associated with the conduct of training, the RN discontinued pressurised submarine escape training in March 2009.