What is a soil pipe used for in plumbing?

A soil pipe is specifically designed to transport human waste from fixtures such as toilets to the drainage system. This type of pipe is crucial in a plumbing system, as it ensures that sewage and human waste are efficiently and safely moved away from living spaces, preventing any health hazards associated with waste accumulation.

This is distinct from the other options. For instance, pipes that carry wastewater from sinks or other fixtures are known as waste pipes, whereas soil pipes are concerned primarily with human waste. Connecting appliances to the gas supply falls under gas piping, which is entirely unrelated to waste drainage. Venting is performed by vent pipes that allow air to enter the plumbing system to facilitate proper drainage and prevent vacuum issues, again not directly involving the primary function of a soil pipe. Thus, the specific role of transporting human waste makes the chosen answer correct.