What is meant by “drain line” in gas appliance terminology?

In gas appliance terminology, a "drain line" specifically refers to a pipe designed to carry condensate away from an appliance. This is particularly important in appliances that produce water as a byproduct of combustion, such as high-efficiency condensing boilers or water heaters. These appliances generate condensate when the combustion gases cool and moisture forms, which needs to be drained safely to prevent water damage or other hazards.

Understanding the function of a drain line is essential for proper installation and maintenance of gas appliances. It ensures that condensate is effectively removed from the appliance and does not accumulate, which could lead to operational issues or potential safety concerns. The other options describe different types of pipes that do not closely align with the specific function of removing condensate from a gas appliance, which clarifies why option C is the most accurate description of a drain line in this context.