<prompt> Septic tank is used for:Excreta disposalStorage of instrumentsPrevent contamination of waterComposting  <response>: Ans: a Excreta disposal Ref: Park 19ed, p. 615A quite simple one! 1 think no explanation is needed. Lets discuss other important related points.Methods of excreta disposalUNSEWERED AREA1 Service type conservatory system2 Non service type sanitary latrinesBorehole latrineDugwell or pit latrineWater seal type, eg: RCA type. PRA1 typeSeptic tankAqua privy3 Latrine suitable for camps and temporary useShallow trench latrineDeep trench latrinePit latrineBorehole latrineSewered areasWater cairi age system and sewage treatmenta Primary treatmentScreeningRemoval of gritPlain sedimentationb Secondary treatmentTrickling filterActivated sludge processc Other methodsSea outfallRiver outfallSewage fanningOxidation pondTrickling filter- zoological layer- smaller cities Activated sludge process - aeration tank is the heart- for larger cities 