While in dry-dock, what means are provided for completely draining the double bottom tanks in preparation for inspection?

Correct Answer: Option D — Docking plugs.

Docking plugs are threaded fittings installed at the lowest point of double-bottom tanks. When a vessel is in dry-dock, these plugs are removed to facilitate the complete drainage of residual liquids, allowing for thorough internal inspection and cleaning as required by regulatory maintenance standards.