The line of Taco Tank Fittings provide effective air control in hydronic systems. The fittings maintain adequate air cushion to provide sufficient pressurization against all fluctuations of water volume. Since air can be absorbed in water, the Taco Tank Fitting maintains collected air within the pressure tank. All free and entrained air collected by an air separator or other air collection device is routed through the Taco Tank Fitting, allowing air to pass freely into the pressure tank. The fitting also restricts gravity flow of water between the tank and the system, resulting in lower tank temperature that minimizes reabsorption of air. A unique feature of the Taco Tank Fitting is a single handle shut-off that readily admits additional air cushion into the pressure tank, if necessary.