What is the fitting or device that provides a liquid seal to prevent sewer gas emission?

The fitting or device that provides a liquid seal to prevent sewer gas emissions is a trap. Traps are specifically designed to hold a small amount of water, which acts as a barrier or seal against sewer gases. This water seal is crucial as it prevents harmful gases, which are a byproduct of wastewater decomposition, from entering living spaces and ensures the health and safety of the occupants.

Traps are commonly located beneath sinks, bathtubs, and other plumbing fixtures, where they effectively serve the dual purpose of allowing wastewater to flow through while simultaneously blocking any gas escape.

In contrast, filters, separators, and diverters are designed for different purposes. Filters are typically used to remove solid particles from a liquid, separators are used for segregating different substances (like oil and water), and diverters are intended to guide the flow of liquids from one line to another, but none of these devices provide the liquid seal that traps do. Therefore, traps are the essential components that serve to prevent sewer gas emission effectively.