Every dry vent connecting to a horizontal drain must connect to the drain at what location relative to the drain pipe's center line?

In plumbing systems, it is crucial for dry vents to connect to horizontal drains at the correct location to ensure proper venting and drainage performance. When a dry vent connects to a horizontal drain, it must do so above the center line of the drain pipe. This positioning allows for effective air flow into the drainage system and helps prevent the formation of traps or blockages that can occur if a vent connects below the center line.

Connecting the dry vent above the center line allows the vent to function as intended, equalizing pressure and promoting the smooth movement of water through the drain. This arrangement helps to minimize the risk of siphoning, which could disrupt drainage and cause issues in wastewater management.

The other potential connection points would not achieve the same effectiveness for the venting system. Connecting at or below the center line could lead to problems with drainage efficiency, making it essential to adhere strictly to this guideline in residential plumbing practices.