A plumbing expert explains when it’s safe to pour boiling water in the sink, along with tips to protect your pipes.Credit: SBenitez / GettyKey TakeawaysIt is safe to pour boiling water down the sink drain if the pipes are metal. It flushes away grease and other drain debris.If the pipes are PVC or plastic, rather than metal, they can be weakened over time by boiling water, leading to leaks.Running cold water alongside boiling water doesn’t prote…