Final answer:
The only permitted type of fixture trap in plumbing is the P-trap, which is designed to prevent sewer gases from entering through drains.
Step-by-step explanation:
The only type of fixture trap permitted is a P-trap. A P-trap is the type of trap used in plumbing to prevent sewer gases from entering the building through a plumbing fixture's drain. It is called a P-trap because its shape resembles the letter 'P' when viewed from the side. The only type of fixture trap permitted is a P-trap.
A P-trap is a U-shaped pipe that is installed beneath sinks, showers, and other fixtures to prevent sewer gases from entering the building. It works by trapping water in the U-bend, which forms a barrier against the gases. The P-trap works by maintaining a small amount of water in the trap, which acts as a seal to block the gases. This design is widely accepted and enforced by building codes across many jurisdictions.