The correct answer is D) if discharge is led to a shore tank or barge. The reasoning is that when pumping bilges while a vessel is in port, the discharge should be led to a shore tank or barge to prevent pollution of the surrounding waters. Discharging bilge water directly into the harbor or other waterways is generally prohibited, as it can introduce oil, fuel, and other contaminants into the environment. By directing the discharge to a shore-based containment system, the bilge water can be properly processed and disposed of in an environmentally responsible manner. The other options are incorrect because: A) pumping on a specific tide does not address the need to contain the discharge, B) pumping only "as much as is necessary" does not prevent all potential pollution, and C) pumping during darkness does not change the requirement to properly dispose of the bilge water.