Snorkel

Definition: At its most basic a snorkel is a plastic tube that allows you to breathe while you're swimming on the surface. It is normally attached to the left side of the mask. It's a great way to conserve the air in your cylinder while swimming on the surface. Snorkels also come with such features as purge valves (to make it easier to clear any water inside) and splash guards (to make it hard for water to splash in the top).