I was just cleaning my 6 gal BB primary, after transferring a batch of BM's Centennial Blonde to secondary, when I had a rare "lightbulb" moment. I had soaked the BB overnight with 2 large scoops of Oxyclean. Everything cleaned up nicely with the exception of the remnants of the ring near the top left by the krauesen. I started thinking, OK now I have to fill the whole thing up again and dump 2 more scoops of Oxyclean in. But, I use the ported bottles. I just filled up the bottle with enough water and Oxyclean to cover the stubborn ring when the bottle was inverted. I then turned the bottle upside down and set it in my carboy dryer stand and opened the port to vent the excess pressure. I don't think I would try this with a non ported bottle though. You might build up enough pressure to eject the closure, with an accompanying mess.
