Which tool is used to turn off water and drain a line?

The tool used to turn off water and drain a line is known as a pipe stop and waste. This device is specifically designed for use in plumbing systems and serves a vital function in managing water flow. When installed in a pipeline, it allows for easy isolation of water flow for maintenance or repair work. Additionally, it facilitates draining the line, which is crucial to prevent freezing in cold temperatures or to clear the line for repairs.

The other tools listed serve different purposes: a pipe union is used to connect two sections of pipe, facilitating easy disconnection when needed; a pipe wrench is designed to grip and turn pipes during installation or repairs but does not control water flow; and a piston ring compressor is used in automotive applications for installing piston rings and has no relevance to plumbing tasks. Understanding the specific functionalities of each tool helps determine the correct one for the task of managing water lines.