What is a rubber or plastic tube used to drain or inject fluid through a body opening called?

The term for a rubber or plastic tube used to drain or inject fluid through a body opening is a catheter. Catheters are medical devices designed for specific therapeutic and diagnostic purposes. They can be used to deliver medications, drain fluids, or perform various procedures involving bodily openings such as veins or the urinary tract.

Syringes are instruments for drawing in or ejecting liquids, typically used for injections but do not serve the role of a continuous drain or conduit for fluid. Aspirators are devices used to remove fluids or gases from a body cavity but are not tubes meant to be inserted into the body. Conduits refer more generally to channels or tubes used for guiding other substances, but they do not specifically denote the medical equipment designed for draining or injecting fluids as catheters do. Hence, the specificity of the function and design of a catheter makes it the correct answer.