Bring 2–4 cups of water to a rolling boil.

Quickly cover the drain opening with a plug or a damp cloth. This traps the expanding foam inside, forcing the reaction deeper into the pipe rather than letting it bubble back up.

Remove the cover. Boil another 2–4 cups of water (or run the hottest tap water for 1–2 minutes) and flush the drain thoroughly.

Slowly pour the boiling water directly into the drain to soften and loosen grease, soap scum, and debris.

Let the mixture work. For tough clogs (e.g., hair and soap), wait 30 minutes or even overnight. You’ll hear occasional fizzing.

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