Which combining form refers to the act of washing or flushing?

The combining form that specifically refers to the act of washing or flushing is "-clysis." This term is derived from the Greek word “klysis,” which means "washing" or "to wash." In medical terminology, it relates to the process of administering fluids through various routes in order to cleanse or flush out an area, often in the context of hydration or treating dehydration.

Other options, while relevant in different contexts, do not convey the act of washing or flushing. For instance, "hydro/o" pertains to water and is used in terms related to water or fluids but doesn't explicitly denote the act of washing. Similarly, "-lysis" refers to the breakdown or destruction of substances, often seen in processes such as the dissolution of cells. "-phoresis" relates to the movement of substances across a membrane, typically seen in contexts involving the transfer of ions or compounds, but it does not imply washing. Therefore, "-clysis" accurately describes the action in question.