Ebonstone Wall

This counts as corrupt background, and corrupt background creeps into whatever pure walls sit next to it. In a corruption themed build that is fine. In the middle of a base it is a slow disaster you will not notice until the biome check flips and your NPCs start refusing to move in. If you want the look without the consequences, fence the patch off the same way you would fence off an infected biome.

The Clentaminator sprays a wide cone, so it is a blunt instrument for wall work. You will convert blocks and neighboring wall types you meant to leave alone, and undoing that costs another pass with the opposite solution.

Unholy Water is the accurate option. It covers a much smaller footprint, so you can outline a small corrupted section without repainting the whole room around it. Slower, but you spend less time fixing overspray.