Section 83(3)(ii) in Assam Notified Urban Areas (Other than Guwahati) Building Rules, 2014
(ii)the tank shall be large enough to hold twice the expected daily flow of wastewater plus 40% to allow sludge accumulation and surge loading. One type of settling tank well suited for grey water treatment is a septic tank with aeration facility. (area requirement approx. 8 sq.m per m3 of wastewater)