Leave just enough water to cover the drain hole. Pour 1 cup (250g) of caustic soda flakes directly into the toilet bowl, aiming for the drain opening.

When in doubt, throw the lye away and snake it out. Your plumbing (and your skin) will thank you.

There’s a mess in the bathroom. The water level is high, the plunger has failed, and the chemical drain cleaners under the sink look suspiciously mild. You’ve heard rumors about a "nuclear option" for plumbing: Caustic Soda.

Once the drain is flowing, flush the toilet three times to ensure all caustic residue is gone. Do not urinate in the toilet for an hour (urine is acidic and can react with remaining lye to release fumes). The Final Verdict Use caustic soda as a last resort before calling a professional—not as a first response.