Search: "sodium hydroxide" porcelain enamel corrosion or "caustic soda" PVC pipe degradation Toilets are vitreous china (acid/alkali resistant but prolonged high-concentration NaOH can etch glazing). PVC is generally fine up to ~50°C and moderate NaOH.
Never mix caustic soda with other drain cleaners. If you have previously tried a different acid-based cleaner (like sulfuric acid drain openers) and follow it with caustic soda, it can create an explosive reaction, releasing chlorine gas or causing a violent eruption in the bowl. caustic soda toilet
: Sodium hydroxide is highly corrosive to aquatic life and can disrupt the pH balance of local water systems if it enters the wastewater stream in large quantities. Safer Alternatives it can create an explosive reaction