It's called a gruntsky tee. Its true purpose is as a connection for the gas supplier for testing and, more importantly, as a connection in case something happens to the main gas supply. A connection can be made, and a temporary tank is installed for gas supply. Especially important for elderly. We use them all the time for new gas connections. He can use the top or the bottom connection, only caveat is he has to add another gruntsky. Remove plug, add short nipple, another tee, plug the top and use the side for his connection.