A Compression Tee (a.k.a. coupling) is a fitting that’s been specially designed for joining any metal or PVC pipes or tubes in your building together. This is why they’re sometimes sold as “pipe repair couplings.”
Primarily used for underground connections, this fitting uses a rubber gasket that’s compressed against the existing pipe once tightened into place. This will create a leak-free seal without you needing to thread, glue, or solder the pipe’s connection.
While you can use metal above ground level, PVC is typically used below ground. When using PVC in this way it’s important to make sure to install it below the frost level. You also don’t want to use this on a pipe that’s heavily corroded, rusty, or pitted because then it may leak. Some professionals also say that this is a good reason not to use these on older steel or galvanized steel pipe.