A pluming fitting and adapter for coupling a tubing to the plumbing fitting. The adapter has first and second adapter end portion with connected fluid passageways. The second adapter end portion being insertable into the free-end portion of the tubing. A pluming fitting housing has a chamber sized to receive the first adapter end portion. When the first adapter end portion is positioned within the chamber, an outer end portion of its fluid passageway is in fluid communication with the chamber. A seal and gripper ring within the chamber seal with and releasably grip the first adapter end portion.