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.
You cannot pour caustic soda into a toilet full to the brim. Use an old cup or scoop to remove most of the standing water into a bucket (dispose of this dirty water outside or down a sink after the toilet is fixed). caustic soda for blocked toilet
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. There’s a mess in the bathroom
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. You cannot pour caustic soda into a toilet full to the brim
If your blockage is organic—think a "mountain" of waste, wet wipes (that aren't really flushable), or a slow-draining toilet due to biofilm buildup—lye will dissolve it.
When in doubt, throw the lye away and snake it out. Your plumbing (and your skin) will thank you.
Also known as sodium hydroxide (NaOH) or lye, this industrial-strength chemical is a staple in soap making and commercial cleaning. But can it actually solve a toilet clog? The short answer is yes —but with enough caveats to fill a hazard suit.