Where should the vent be taken off from the horizontal drain pipe?

The vent should be taken off from the horizontal drain pipe above the centerline of the pipe to ensure effective venting. When the vent is positioned above the centerline, it allows for proper air flow in the plumbing system, which is essential for maintaining atmospheric pressure and preventing the creation of siphons that could disrupt drainage. Proper venting ensures that wastewater can flow freely without creating a vacuum, which could impede drainage and lead to potential blockages or backups.

Additionally, positioning the vent above the centerline helps to align with plumbing codes, which are designed to provide guidance on proper practices and ensure the safe and efficient operation of plumbing systems. This practice also aids in minimizing the risk of venting issues, such as foul odors escaping into the living space or inadequate pressure equalization.