Which of the following specifications of a septic tank is INCORRECT?
1
Floor should be given a slope of about 1 in 20 for the convenience of collection and removal of sludge.
2
Septic tank usually consists of brick wall in cement mortar not less than 20 cylthick and the foundation floor is of cement concrete 1 ∶ 3 ∶ 6 or 1 ∶ 2 ∶ 4.
3
Septic tank is so designed that the sewage is retained in the tank for 24 hours and clear water flows out of the septic tank.
4
Septic tank is constructed with lining of dry brick or stone with open joints backed with at least 7.5 cm thick coarse aggregate.