Next, learn about the basic fittings used for a typical system assembly. Like the flexible tubing, these components are molded from polyethylene. Featured pieces include: The straight coupler (Image 1). This fitting is used to connect two pieces of pipe that meet at a certain point or to extend a length of pipe that's too short to reach the necessary area. The poly plug (Image 2), shaped, appropriately, like a stop sign, is used at the end of a pipe length to stop water at a designated point. The elbow coupler (Image 3) is sometimes referred to simply as a "90", since it creates a 90-degree angle in a system of pipes. In short, it's used to change the direction of the water, allowing the system to turn a corner. The T-coupler (Image 4) fitting is designed to join together three pipes at one intersection, either coming off a main line or leading to a valve. To control the release of the water into the pipes, electronic valves (Image 5) are integrated into the system.