Boiling Water Down Drain [TESTED]

Even if the pipes are metal, the rubber or plastic seals and the glue used at joints can be damaged or loosened by the extreme heat. Ineffective for Deep Clogs:

Every sink has a P-trap—the curved pipe under the basin that holds water to block sewer gas. P-traps are often made of thin metal (like chrome-plated brass) or plastic. Because they hold standing water, pouring boiling water into the sink means that water will sit in the P-trap, soaking the same small section of pipe with intense heat. Thin metal P-traps can warp, and plastic ones can soften and droop, leading to leaks. boiling water down drain