A plumbing drain trap is designed to retain a small amount of water each time the sink drains, and this water standing in the bottom of the curved portion of the trap seals the drain and keeps sewer gasses from escaping the drain and entering your home.

Is a drain trap necessary?

Yes, shower and tub drains require a trap in the plumbing to prevent harmful sewer gases from coming into the home.

What does a Ptrap do?

A P-trap Prevents Odors The curve in P-Trap always retains water. Water is trapped at the bottom of the curve — hence the name. This small volume of water prevents sewer gases from entering your bathroom, sparing your nose from nasty odors and protecting your health.