A client complains of a persistent, sewage-like odour emanating from their basement floor drain, even though the drain appears clear and there's no standing water. Which of the following is the most likely cause?

Question: A client complains of a persistent, sewage-like odour emanating from their basement floor drain, even though the drain appears clear and there's no standing water. Which of the following is the most likely cause?

Answer options:

• A blockage deep within the main sewer line
• A cracked foundation allowing sewer gas infiltration ✅ The floor drain's trap primer is not functioning, or the trap has evaporated
• A septic tank that needs to be pumped

Correct answer: The floor drain's trap primer is not functioning, or the trap has evaporated

Explanation: A sewage odour from a clear floor drain most commonly indicates that the trap's water seal has evaporated or the trap primer (if present) is not working, allowing sewer gases to enter the building. A main sewer line blockage would usually cause backups, and a cracked foundation less commonly causes localized drain odour without other symptoms.