Do gator bites work on existing plumbing? I have a T connection in a real tight location that is leaking, it would be a great solution, but the directions say to twist in place. That would be impossible. Do they need to be twisted to make the seal?

No, not at all. It just makes it easier to push them on. Twisting or not, they will seal up the same. Just push the pipes strait in and you should be all set. Please let me know how things work out.