Section 29(2) in The Merchant Shipping (Prevention of Pollution by Oil from Ships) Rules, 2010
(2)In respect of an oil tanker referred to in sub-rule (1),-(a)Adequate means shall be provided for cleaning the cargo tanks and transferring the dirty ballast residue and tank washings from the cargo tanks into a slop tank approved by the Central Government;(b)in such system, arrangements shall be provided to transfer the oily waste into a slop tank or combination of slop tanks in such a way that any effluent discharged into the sea will be such as to comply with the provisions of rule 35;(c)the arrangement of slop tank or combination of slop tanks shall have a capacity necessary to retain the slop generated by tank washings, oil residues and dirty ballast residues and the total capacity of the slop tank or tanks shall not be less than three percent of the oil-carrying capacity of the ship, except that the Central Government may accept,-(i)2% for such oil tankers where the tank washing arrangements are such that once the slop tank or tanks are charged with washing water, this water is sufficient for tank washing and, where applicable, for providing the driving fluid for educators, without the introduction of additional water into the system;(ii)2% where segregated ballast tanks or dedicated clean ballast tanks are provided in accordance with rule 18, or where a cargo tank cleaning system using crude oil washing is fitted in accordance with rule 33:Provided that this capacity may be further reduced to 1.5% for such oil tankers where the tank washing arrangements are such that once the slop tank or tanks are charged with washing water, this water is sufficient for tank washing and, where applicable, for providing the driving fluid for educators, without the introduction of additional water into the system; and(iii)1% for combination carriers where oil cargo is only carried in tanks with smooth walls:Provided that this capacity may be further reduced to 0.8% where the tank washing arrangements are such that once the slop tank or tanks are charged with washing water, this water is sufficient for tank washing and, where applicable, for providing the driving fluid for educators, without the introduction of additional water into the system;(d)Slop tanks shall be so designed, particularly in respect of the position of inlets, outlets, baffles or weirs where fitted, so as to avoid excessive turbulence and entrainment of oil or emulsion with the water.
