Ex-McDonalds Employee here. First off, working at McDonald's for a first job is an excellent choice. You learn how to deal with customers from all walks of life and better prepares you for future careers.
Back on topic, those bags are in there because the inside of the urns isn't stainless steel, only the outside so the inside tends to rust. The bags sit in there, are replaced everyday (should be) and have a little dick that you pull through the front where the tea pours out. When you make tea you set the urn up under the brewer, put a bag of tea in it and it run hot water through, then you add an ENTIRE bag of sugar. ONE WHOLE BAG OF SUGAR FOR ONE URN, and you wonder how tea can be so bad for your health.