What is the purpose of a P trap in plumbing system?

Answer 1

Fixture trap is a fitting designed and constructed as to provide liquid seal that will prevent the back passage of air from sanitary system without affecting the flow of sewage or waste water through it.  

Fixture traps have following characteristics:

• Self – cleaning
• Smooth interiors
• No movable parts or partitions
• Minimum 2 inch seal
• An accessible cleanout

Answer 2

The purpose of the trap is to hold water to prevent sewer gases containing viruses and bacteria from entering the home through the drain.