Push in fittings are a popular alternative to traditional fittings and are suited for plumbing systems such as potable water, hydronic heating systems, irrigation, and water heaters. No specialist tools are required and they're much quicker to fit than other fittings. Just push the tube into the fitting to create a strong seal. Push In Union Tee Fittings are used for a variety of applications including connecting a new tube line to an existing tube line at a 90 degree angle.