Septic tank
While a properly maintained and located septic tank does not pose any more environmental problems than centralized municipal sewage treatment, certain problems can arise with septic tanks in unsuitable locations. Since septic systems require large drainfields, they are not suitable for densely built areas.
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.