A tenant in an apartment building reports that their kitchen sink is draining very slowly, and they can hear gurgling noises from the adjacent dishwasher when the sink is used. The building is fairly old, and the tenant mentions occasional food scraps going down the drain. What is the most probable cause of this issue?

Question: A tenant in an apartment building reports that their kitchen sink is draining very slowly, and they can hear gurgling noises from the adjacent dishwasher when the sink is used. The building is fairly old, and the tenant mentions occasional food scraps going down the drain. What is the most probable cause of this issue?

Answer options:

• A blockage in the main building sewer lateral.
• An air lock in the P-trap of the kitchen sink. ✅ A partial blockage in the kitchen sink branch line.
• A faulty air admittance valve (AAV) for the kitchen fixtures.

Correct answer: A partial blockage in the kitchen sink branch line.

Explanation: Slow draining and gurgling specifically at the kitchen sink and dishwasher, which share a common branch, typically indicate a partial blockage within that branch line, often due to grease and food debris. A main sewer lateral blockage would affect multiple fixtures throughout the building, and an AAV issue primarily causes suction and slow drainage rather than gurgling with water usage.