Where should a circuit vent or loop vent be placed to effectively serve a battery of fixtures?

The placement of a circuit vent, or loop vent, is crucial for the effective drainage of a battery of fixtures. Having the vent positioned between the upper two fixtures allows for the proper functioning of the drainage system by ensuring that any air and gases can escape efficiently. This configuration helps maintain a balanced atmospheric pressure within the drainage system, preventing vacuum conditions that can lead to slow drainage or the siphoning of traps.

When the vent is located between the upper fixtures, it can effectively serve both fixtures, allowing for the flow of air to assist in drainage without interfering with their function. This strategic placement enhances the overall performance of the plumbing system, ensuring that water flows correctly while also providing the necessary ventilation to prevent blockages or backups.

In contrast, positioning the vent at the base of the fixtures or directly above the highest fixture may not facilitate proper air circulation necessary for these lower fixtures. A vent alongside vertical drains is more suited to draining systems rather than effectively serving multiple fixtures, as it may not address the ventilation needs of the entire fixture battery comprehensively.