An adapter for drainage hole includes a main body having at least one opening defined in a top portion thereof, wherein the main body is a tubular structure. The adapter includes a converging structure radially extending from a lower portion of the main body, wherein multiple converging holes are defined in the converging structure. A fixing structure longitudinally extends from the lower portion of the main body and is adapted to be secured on a filter that is secured in the drainage hole. The converging structure is skirt-shaped and the converging hole is arched-shaped. The fixing structure includes multiple insertions that extend through the filter and extend into the drainage hole for holding the main body in place.
