Abstract: An improved tubing adapter or coupling apparatus, and combination of same with other fittings, is characterized by an adapter member having a first end including at least one exterior barb for engagement with tubing and a sleeve member operatively positioned around the adapter. In some systems, the tubing or hose may include a fitting at its other extremity, such as a hose end, an ell, or another coupling. The sleeve member of the coupling apparatus preferably includes one or more view ports. The ports can enable the user to visually confirm the tubing has been properly and completely assembled onto the adapter member, and, following initial assembly, to visually ascertain the position of the tubing on the adapter. The apparatus also preferably includes corresponding engagement detents on the adapter and sleeve member, for initial engagement of the retaining member with the adapter member prior to assembly with tubing.