Which of the following is true regarding the connection of multiple vent pipes?

The statement that manifolding is allowed regarding the connection of multiple vent pipes is accurate. Manifolding refers to the practice of using a single outlet where multiple vent pipes connect, allowing for a more efficient use of space and materials while ensuring that the venting system remains functional. This approach can simplify the installation process and reduce costs while still adhering to safety and operational standards.

In applications involving vent pipes, manifolding can help manage the exhaust of combustion gases or ensure proper ventilation in a system. Proper manifold design takes into account factors such as the possibility of backdrafts and the need for adequate airflow, making it a practical solution for certain configurations.

The other options do not align with standard practices. For instance, requiring equal sizing for pipes does not necessarily apply, as the size of the vent pipes can vary based on the specific requirements of the system they are venting. The idea that each pipe must be manually operated is also not standard; numerous automated systems are in place that can streamline operation. Finally, the notion that they require separate outlets conflicts with the accepted practice of manifolding, where multiple vent pipes can efficiently share an outlet.