Where must vents be connected to horizontal pipe?

Vents must be connected to horizontal pipe above the center line to ensure proper venting and drainage. This position allows for the effective release of air from the drainage system, preventing pressure buildup and ensuring that wastewater flows smoothly without obstacles. When the vent is placed above the center line, it helps maintain a consistent flow by allowing air to enter the drainage system, which balances the pressure as water moves through the pipes. Proper venting is crucial to prevent siphoning and the backflow of wastewater, which could lead to clogs and other plumbing issues.

Connecting the vent below the center line or at the center line does not provide the same benefits, as it may obstruct air flow or lead to potential siphoning effects. Connecting on the side could lead to inadequate venting as well, since it may not facilitate the necessary pressure equalization within the system. Thus, positioning the vent above the center line serves both functional and compliance purposes in plumbing systems.