Section 30(6)(b) in The Merchant Shipping (Prevention of Pollution by Oil from Ships) Rules, 2010
(b)oil tankers delivered on or before 31st December, 1979, as defined in sub-rule (46) of rule 1A, which, without modification, are not capable of discharging segregated ballast above the waterline, may discharge segregated ballast below the waterline at sea, provided that the surface of the ballast water has been examined immediately before the discharge to ensure that no contamination with oil has taken place;