The _______ connector should enter at the highest level where two or more vent connectors enter a common gas vent, chimney flue, or single-wall metal pipe.

The correct answer is that the smallest connector should enter at the highest level where two or more vent connectors converge. This is crucial because ensuring that the smallest vent connector is positioned highest helps maintain proper airflow and minimizes the risk of back drafting. When the smallest connector is elevated, it allows any potential blockages or lower pressure areas to be alleviated, which is essential for efficient venting of gases. Moreover, this configuration helps to maintain an effective rise in the vent system, facilitating ventilation and preventing the accumulation of harmful gases.

Arranging the smallest connector at the highest point also aligns with the principles of gas venting systems, where larger connectors can handle a greater volume of exhaust gases. This setup ensures that the smallest path remains unobstructed, reducing the chances of interference and optimizing the overall performance of the venting system. Additionally, having the smallest vent above the others assists in balancing the pressure throughout the venting system, a critical factor in ensuring safety and efficiency in gas appliance operations.