I've been soldering since 1902, I think, but once in a while with old work, whether it's old copper or something unseen, I have fought to nail that last $@#& drip, made multiple trips to get clean new fittings, even the ones with solder rings, wasting so much time... Anyway, these fittings seem to be a great answer.. Not cheap, but sometimes our time or frustration levels are worth it!
Check the video, looks good...
http://www.sharkbiteplumbing.com/
- -