Which type of building drain conveys both sewage and storm water?

The type of building drain that conveys both sewage and storm water is known as a combined building drain. This system integrates both waste from sanitary sources (like toilets and sinks) and stormwater runoff into a single drainage system.

The purpose of a combined building drain is to efficiently manage different types of wastewater within a unified system, which can help reduce the overall infrastructure needed for separate systems and can streamline the treatment process. However, it's important to note that modern standards and regulations often encourage the separation of these systems to prevent issues like overflow during heavy rain or contamination of stormwater by sewage. This choice is rooted in historical practices and specific applications, making the combined drain relevant for understanding various plumbing configurations.

In contrast, other types of building drains are designed for more specific purposes, such as strictly handling either stormwater or sanitary waste, which is why they do not fit the description provided in the question.