Drain cleaner is generally a caustic chemical such as strong acid, caustic soda, or lye, in a crystalline or liquid form, used to dissolve clogs in plumbing. It is used to release stoppages in sinks, bathtubs, toilets, and showers. It is often used after a plunger has not been sufficient to finish the job.

Drain cleaner should only be used according to the manufacturer's specifications, as improper use may cause burns to skin, cause respiratory problems or damage lungs, or cause damage to eyes.

Popular brands of drain cleaner include Draino and Liquid-Plumr.

The product, especially Draino, has gained infamy as a horrific weapon of murder, the victim forced to ingest it.