And with Lub oils dont wait for the overboard to slam shut at 30 litres / nautical mile- by which time your sensor is already dirty. The modern ODMCS units do NOT have sensor cleaning soap/ emulsifier solution -- as this soap foam solution inside the decanted slop can be rejected .
Alter course and run the steam coils to keep the oil interface right on the surface of the slop to be decanted.
Finally this decanted ROB must be stripped into the deck tank as long as it is in the IOPP certificate form B , so that you do NOT waste a slop cargo tank on a ANNEX 2 chemical tanker. If this deck tank is epoxy coated--you can use salt water for washing instead of fresh water. The deck tank slop content can be carried till you reach an economical port.
In the ORB mention that you used 2 pass ,when you use limited fresh water.