All are features of septic tank except:

SEPTIC TANK: Is a water-tight masonary tank into which household sewage is admitted for treatment Is a satisfactory method of disposing liquid and excreta wastes from individuals dwellings, small groups of houses or institutions which have &;adequate water supply but donot have access to a public sewerage system&; Design features of a septic tank: Ideal retention period: 24 hours Steps of purification in a septic tank: Anaerobic digestion: Takes place in septic tank proper Aerobic oxidation: Takes place in sub-soil (outside septic tank) Ref: Park 25th edition &; Pgno: 797