33 C.F.R. § 157.28
Discharges from tank barges exempted from certain design requirements
The person in charge of a tank barge exempted under § 157.08(g) from the requirements in §§ 157.11, 157.13, 157.15, and 157.23 shall ensure that while the barge is proceeding en route:
(a) Cargo tanks are not ballasted or washed; and
(b) Oil or oily mixtures are not discharged.