When connecting plastic pipe to metal pipe, what should be used?

Using a plastic adapter with internal threads is the appropriate choice when connecting plastic pipe to metal pipe. This method ensures a secure and leak-free connection that accommodates the different materials' properties.

A plastic adapter allows for compatibility with plastic pipe, which offers chemical resistance and flexibility. The internal threads of the plastic adapter can readily accommodate the external threads of the metal pipe, ensuring a safe and effective connection. This approach is particularly important because it helps prevent stress and potential cracking in the plastic due to mismatched thermal expansion rates between the metals and plastics.

In contrast, other options might present risks or complications. A metal adapter with external threads could lead to corrosion issues due to differing material properties. A rubber gasket may not provide a strong enough mechanical connection for high-pressure systems. Lastly, attempting a direct connection without any adapter could compromise the integrity of the joint, resulting in leaks or failures over time.