821. (1.2.15-9) On US flag steam propulsion vessels, the main reason for having a low suction line on the fuel oil service or settling tanks is to accomplish which of the following?

A low suction line on fuel oil service or settling tanks is designed to facilitate water removal, as water and sludge accumulate at the lowest point of the tank and require separate removal to maintain fuel quality and protect machinery; this is the primary purpose, distinct from pump performance or fuel availability.