What is the minimum height at which a vent can be tied in above the highest fixture?

The minimum height at which a vent can be tied in above the highest fixture is established to ensure proper venting and airflow within the plumbing system. The chosen answer reflects the code requirement that dictates that a vent must be installed at least 6 inches above the flood rim of the highest fixture served. This measurement helps prevent the potential for wastewater to backflow into the vent, which could compromise the system's ventilation and lead to improper drainage.

By placing the vent at this height, you ensure that the plumbing system can effectively remove air and gases that accumulate, thus maintaining hydraulic efficiency and preventing siphoning in the drainage system. It is essential for this height to be adhered to in order to comply with the Massachusetts Plumbing Code, which sets specific standards to protect public health and safety.