To thaw frozen drain pipes, apply heat using a heat gun, thaw cable, hairdryer, or boiling water. Alternatively, use chemical drain cleaner, baking soda, or vinegar to dissolve ice. Take safety precautions by avoiding chemical exposure, burns, and ensuring proper ventilation. Insulate pipes and walls/ceilings, and open faucets when temperatures drop below freezing to prevent future freezing. Plumbers can also assist with complex or persistent issues, while regular drain cleaning and home maintenance can minimize the risk of frozen pipes.