If a rear differential lacks a drain plug, which tool may be required to service the fluid?

• A. Siphon
• B. Gravity drain
• C. Suction gun
• D. Pump

Answer: (C)

When there is no drain plug, you need a way to remove the old gear oil through the existing opening, and a suction gun is designed for that job. It uses a hand pump to pull fluid up through a tube inserted into the differential (often via the fill hole) into a container. This lets you evacuate most of the old oil without a bottom drain path and fits into tight spaces where gravity flow or simple siphoning isn’t reliable. A siphon can be tricky to start and may not drain completely through a small fill opening; gravity drain isn’t possible without a lower outlet; a pump is mainly for moving fluid in or out but doesn’t provide the necessary suction path through the case opening. So the suction gun is the best tool for removing fluid when there’s no drain plug.