Which type of pipe is considered the best for underground drains within buildings?

Cast iron pipe is considered the best choice for underground drains within buildings due to its durability and strength. It can withstand high pressures and loads, making it suitable for underground applications where it may be subject to external forces from the surrounding soil, vehicles, or other structures. Cast iron also has excellent sound-dampening properties, which is important in reducing noise from the drainage system. Additionally, cast iron is resistant to corrosion when properly maintained and can have a long lifespan, making it a reliable option for plumbing systems that are buried and not easily accessible for repairs or replacements.

While plastic pipe is lightweight and resistant to corrosion, it may not provide the same structural integrity or longevity as cast iron in underground settings. Copper pipe, while known for its corrosion resistance, is typically more expensive and not as commonly used for drainage purposes. Acrylic pipe is not standard for underground drains as it lacks the necessary strength and durability compared to the other materials mentioned.