This Mueller 429-020 2 Coupling PVC Slip X Slip is a two-piece coupling that is designed to connect two PVC pipes. It is made of durable PVC and has a slip joint design that makes it easy to connect and disconnect pipes. This coupling is perfect for use in water, gas, and oil pipelines. This Mueller 429-020 2 Coupling PVC Slip X Slip is a two-piece coupling that is designed to connect two PVC pipes. It is made of durable PVC and has a slip joint design that makes it easy to connect and disconnect pipes. This coupling is perfect for use in water, gas, and oil pipelines.