All gravity horizontal drains within or under a building shall be accessible through a cleanout.

• A. Must be accessible through a cleanout
• B. Must be vented every 40 feet
• C. Must be trapped at every 50 feet
• D. No cleanouts required

Answer: (A)

When drains rely on gravity, blockages have to be reachable for clearing. That’s why horizontal drains inside or under a building must be accessible through a cleanout. The cleanout creates a practical entry point for rodding or cleaning equipment, allowing maintenance without tearing into walls or floors. It also helps with inspection and testing of the line. The other ideas—venting a fixed distance, trapping every so often, or having no cleanouts—are separate concepts and don’t provide the necessary access point for clearing obstructions.