Answer
Under MARPOL Annex I, Regulation 34, any discharge into the sea of oil or oily mixtures from the cargo area of an oil tanker is strictly prohibited except when all the following conditions are simultaneously satisfied:
The tanker is not within a Special Area (e.g., Mediterranean Sea, Baltic Sea, Black Sea, etc.).
The tanker is more than 50 nautical miles from the nearest land.
The tanker is proceeding en route (navigating under its own propulsion).
The instantaneous rate of discharge of oil content does not exceed 30 liters per nautical mile.
The total quantity of oil discharged into the sea does not exceed 1/30,000 of the total quantity of the particular cargo of which the residue formed a part.
The tanker has in operation an Oil Discharge Monitoring and Control System (ODME) and a slop tank arrangement as required by regulations 29 and 31.
MEO Class 1 Tip: Emphasize that if the ODME malfunctions, the discharge must be stopped immediately, the defect logged in the Oil Record Book (ORB) Part II, and it must be reported to the Flag State. The vessel can only manually discharge for a maximum of 3 days under Flag State permission, provided manual line checks and sampling are maintained.