Plain English Meaning

Little drain valves at the bottom of the fuel tanks. You open them during preflight to let out a small cup of fuel, check it for water and dirt, and confirm it's the right type of fuel.

Full Definition

Small valves located at the lowest points of an aircraft's fuel system that allow the pilot to drain a small sample of fuel before flight. Their purpose is to remove water, sediment, and contaminants that have settled to the bottom of the fuel tanks and lines, and to allow the pilot to verify the correct fuel grade and color.

Context Anchor

You encounter fuel sump drains during preflight inspection, especially when checking the fuel tanks and before starting the engine.