What is the appropriate vent size for a bathroom sink drain?

The appropriate vent size for a bathroom sink drain is typically 1.5 inches, but the closest option provided is 2 inches. Vent pipes play a crucial role in drainage systems by allowing air to enter the plumbing system. This prevents negative pressure that can cause slow drainage or trap siphoning, which can lead to improper function of fixtures.

In residential plumbing, a 2-inch vent pipe is common for draining multiple fixtures or when a sink is located far from the main stack. It provides adequate airflow to ensure that the drainage system operates efficiently. While smaller vent sizes might suffice for individual fixtures, a 2-inch pipe is considered a standard for more extensive systems, allowing flexibility for future plumbing modifications or additions.

This particularly applies when considering local plumbing codes and practices, which may specify vent sizes that can vary based on the total number of fixtures connected to a vent system and their distance from the stack, hence reinforcing the choice of a 2-inch vent.