Subject to the provisions of paragraphs 4 and
5 of regulation 3 of this Annex,
oil tankers of 150 gross tonnage and above shall be provided with
effective oil/water interface detectors approved by the Administration
for a rapid and accurate determination of the oil/water interface
in slop tanks and shall be available for use in other tanks where
the separation of oil and water is effected and from which it is intended
to discharge effluent direct to the sea.