4 Inch PVC Sewer & Drain 90 Degree Elbow for SDR-35 S&D Pipe, HUBxHUB. An elbow is a plumbing fitting that allows you to connect two sections of PVC pipe. The fitting has a 90 degree right angle design in order to create a sharp turn in the pipe when needed. It features two 4 inch connections; a slip fit connection on one side (meaning that the pipe slips easily into the elbow fitting) and another slip connection on the other. The fitting is specifically used in order to connect two sections of SRD-35 PVC pipe or fittings. These fittings are great for sewer and drain applications such stack vent (aka. stink stack, soil stack or stink pipe) and other drain applications within a residence or commercial property. However they should NEVER be used for gas or compressed air applications.