Which of the following is NOT a permissible connection for a vent pipe?

Vent pipes play a crucial role in plumbing systems by allowing air to enter the drainage system, which helps to prevent the formation of vacuum, ensuring that wastewater flows smoothly. Understanding permissible connections for vent pipes is essential for the integrity and functionality of the plumbing system.

Connections that allow venting to become a drain are not permissible because they would compromise the primary purpose of the vent system. If a vent pipe were to function as a drain, it could lead to the potential blockage of air flow, causing pressure issues, and allowing sewer gases to enter the living space, which poses health risks.

In contrast, connections made at the highest point of a system are acceptable because this is where the venting is most effective; it allows any potential buildup of gases to escape. Similarly, using approved fittings and maintaining the proper slope are both necessary to ensure that the venting system can function correctly without impediments. Approved fittings ensure that connections conform to codes and standards, while the proper slope facilitates drainage and air flow, preventing condensation and blocking.

The foundational principle of a vent pipe is to ensure airflow while keeping the system separate from the actual drainage of wastewater, and understanding the limitations and requirements for vent connections is critical for proper installation and system performance.