Oily water should be pumped to which of the following locations?

Pumping oily water to the slop tank is appropriate because slop tanks are specifically designated for collecting and storing bilge and oily water mixtures before they are treated or properly disposed of. The slop tank provides a controlled environment for the collection of these waste materials while ensuring compliance with environmental regulations.

This method allows for the oily water to be kept separate from other waste and facilitates easier treatment or disposal later. Regulations regarding the discharge of oily water into the sea require that the oil content be reduced to permissible levels, and the slop tank is an essential part of managing waste in a way that aligns with these regulations, ensuring the safety of marine environments.

In contrast, waste disposal units and bilge wells have different functions and purposes and are not specifically designed for handling oily water in the same way that slop tanks are. The engine room is primarily involved in the operation of machinery and is not an appropriate place for storing or processing oily water due to safety and operational concerns.