Journeyman Plumber ExamDrainage, Waste, and Venting (DWV) SystemsEasy
A plumber is installing a main building drain in a new commercial building. The drain will eventually connect to the public sewer system. Which of the following is the most suitable material for this underground application, considering durability, resistance to corrosion, and common code acceptance?
- ACast Iron (Service Weight)
- BGalvanized Steel
- CSchedule 40 PVC
- DType K Copper
Show answer & explanationAnswer & explanation
Correct answer: A. Cast Iron (Service Weight)
Cast Iron (Service Weight) is a highly durable and widely accepted material for underground building drains and sewers due to its strength, resistance to crushing, and long lifespan. While PVC is also used, cast iron is often preferred for its superior structural integrity in commercial or heavy-traffic areas.
Why the other options are wrong
- B. Galvanized Steel is generally not approved for underground drainage due to its susceptibility to corrosion and eventual failure in soil environments.
- C. Schedule 40 PVC is commonly used but may require additional protection or specific bedding for underground commercial applications, and can be less resistant to crushing than cast iron.
- D. Type K Copper is excellent for water supply, but prohibitively expensive and not typically used for large-diameter drainage systems, especially underground.
Underground Drainage Materials
Materials approved for use in horizontal drainage piping installed below grade, outside or beneath a building structure.
- Must withstand external loads (soil, traffic).
- Must be corrosion-resistant.
- Must be durable for long-term service.
- Common options include cast iron, PVC, and occasionally ABS.
Memory trick: Underground, only Tough pipes Survive.