Pour half a cup of baking soda followed by half a cup of white vinegar down the drain. Plug the drain and let it fizz for 15 minutes, then flush with hot tap water (not boiling).
Even if you have metal pipes, the rubber seals and gaskets inside the P-trap (the U-shaped pipe under the sink) can be degraded by repeated exposure to boiling water, leading to persistent leaks. When Is It Safe to Use? boiling water down drain
Boiling water is a "traditional" remedy that hasn't aged well with modern construction materials. While it is a natural and chemical-free option, the risk of melting PVC joints or cracking a porcelain fixture usually outweighs the benefits. Stick to hot tap water and mechanical methods like plunging to keep your plumbing system intact and leak-free. Pour half a cup of baking soda followed