What is a plumbing trap used for and what types are there?

The trap is an essential plumbing device that creates a water barrier to prevent sewer gases from entering the room. According to the Quebec Plumbing Code:

How it works: Water stays trapped in the trap's curve (water height: 50 to 75 mm), creating a hydraulic seal that blocks odors and gases.

Types of traps:

• P-trap: The most common, used for sinks, lavatories, showers. Diameter: 1 ¼ in (lavatory) or 1 ½ in (kitchen sink)
• S-trap: Prohibited in Quebec for many years — it can self-siphon
• Bottle trap: Used under designer sinks where space is limited
• Floor drain trap: Diameter 2 in to 4 in, often with an odor-proof basket

Rules: Each plumbing fixture must have its own trap. The trap must be accessible for cleaning (via an access panel or cleanout plug). A trap that hasn't been used for more than 6 months may dry out and let odors through — simply pour a liter of water to reactivate it.