This toilet and sink waste pipe is for the upstairs bathroom. After some years, these suddenly became disconnected from the outside down pipe. I am struggling to get them to stay connected, and without there being any leaks. The one the right seems to be okay, but the one on the left leaks and/or comes away. They are on the first floor, and are easily enough accessible with a stepladder. Seems like it ought to be a simple enough job, without needing a plumber. Yet, I am struggling. Any thoughts please?