Section 123(3) in West Bengal Municipal (Building) Rules, 2007
(3)(a)A pipe shall be joined to the sink by a bell mouth at the bottom of the sink having its internal diameter about one inch larger at the sink than at the other ends;(b)the sink outlet shall be fitted with a brass grating and a plug;(c)the sink waste pipe shall have an internal diameter of not less than 5 cm (2 inch) and shall be preferably provided with a trap of drawn lead or other equally suitable material fitted with a brass cleaning screw at the bend.
