Once the job is done, flush the toilet at least three times. This ensures all traces of the sodium hydroxide are washed out of the S-bend and into the main sewage line. Wash your gloves thoroughly with soap and water before taking them off, and wash your hands immediately afterward.

If you are dealing with a persistent blockage or feel uncomfortable handling caustic chemicals, it is best to contact a professional through a service like London Plumber or Thornton & Grooms How To Unblock A Toilet | Staunch & Flow Plumbers

However, always remember: If you are uncomfortable handling dangerous chemicals, or if you suspect a non-organic blockage (like a toy or a toothbrush), call a plumber. Chemicals cannot dissolve plastic.

: Do not mix caustic soda with other cleaners (especially bleach or ammonia), as this can create lethal gases. How to Use Caustic Soda for Toilets

Chemically known as Sodium Hydroxide (NaOH), caustic soda is a highly alkaline compound. While bleach works by oxidizing (breaking down bonds through oxygen), caustic soda works by hydrolyzing. In plain English: it turns organic solids—like hair, grease, soap scum, and paper—into a liquid or soluble goo that can be washed away.

If you aren't dealing with a solid blockage but rather a dirty, stained bowl, you can create a cleaning solution.