If item "1" in the illustrated oily water separator indicates an abnormally deep vacuum, which of the following conditions is the most probable cause? Illustration GS-0153

Correct Answer: Option B — Suction line inlet strainer is obstructed.

An abnormally deep vacuum at the suction side indicates excessive resistance to flow. A clogged suction strainer restricts the intake of bilge water, forcing the pump to work against a vacuum. This is a common operational failure mode in oily-water separators requiring routine maintenance per 46 CFR Subchapter F.