What plumbing feature is necessary to prevent sewer gases from entering living spaces?

The necessary plumbing feature to prevent sewer gases from entering living spaces is a trap.

Traps are plumbing fittings designed to hold a small amount of water, effectively creating a barrier against sewer gases that could otherwise escape into the home. They work by utilizing the water seal—this water barrier blocks the path of gases that could rise from the sewer system into the interior of a building. The presence of a trap is essential in any plumbing system connected to a toilet, sink, or shower.

While other options, such as a sanitary sewer and vent pipe, contribute to effective plumbing and drainage systems, they do not serve the specific and critical function of directly preventing sewer gases from entering occupied areas. A sanitary sewer is responsible for transporting waste away from buildings, and a vent pipe plays a role in equalizing pressure in the plumbing system, allowing for proper drainage. A storm drain is designed to handle surface water from rain, rather than waste or gases. Thus, traps are integral to ensuring indoor air quality and safety by mitigating the risk of foul odors and harmful gases.