This Mueller 406-020 2 90 PVC Ell Slip X Slip is a slip for use with PVC pipe. It has a ell shape and is made of 90% PVC and 10% elastomer. It is designed to protect the pipe from wear and tear and to keep the pipe from sticking to the ground. This Mueller 406-020 2 90 PVC Ell Slip X Slip is a slip for use with PVC pipe. It has a ell shape and is made of 90% PVC and 10% elastomer. It is designed to protect the pipe from wear and tear and to keep the pipe from sticking to the ground.