Does every plumbing fixture need a P-trap?

Yes — each plumbing fixture must be separately trapped by a water-seal trap, with no more than 24 inches vertically from the fixture outlet to the trap (IRC P3201.6).

The IRC requires each plumbing fixture to be served by its own water-seal trap (a P-trap). The vertical distance from the fixture outlet to the trap weir cannot exceed 24 inches (610 mm), which keeps the seal effective.

Fixtures generally cannot be double-trapped, and the trap must hold a liquid seal between 2 and 4 inches deep (IRC P3201.2). That water seal is what blocks sewer gas from entering the home.

A single trap may serve up to three like fixtures — such as a multi-bowl kitchen sink or a set of laundry tubs — within the code's limits.