The science behind this method is simple: hot water helps break down organic material (waste, toilet paper) and can soften grease or fats that might be causing the blockage. In practice, it works best on "soft" clogs—typically an excess of toilet paper or standard waste.
This is the most common mistake. Pouring a pot of rolling boiling water into a cold porcelain toilet bowl can cause the porcelain to crack or shatter due to thermal shock. The water should be hot—roughly the temperature of a very hot bath (around 140°F / 60°C)—but not boiling. It should be hot to the touch but safe enough to dip a finger in. hot water for toilet clog
