Section 30(6)(e) in The Merchant Shipping (Prevention of Pollution by Oil from Ships) Rules, 2010
(e)oil tankers delivered on or before 31st December, 1979, as defined in sub-rule (44) of (rule lA, at sea dirty ballast water or oil-contaminated water from cargo tank areas may be discharged below the waterline, sub-sequent to or in lieu of the discharge, by the method referred to in clause (d) of sub-rule (6):