I'm no expert, just sharing what I did. My old "pre-Sandy" panels were plumbed this way, worked great for many years. If Sandy didn't rip them off my roof I'm sure the panels would still be in use. I had no leaks, absolutely zero operational problems. I just blew them out for winterizing and here on Long Island it can get into the single digits during Jan/Feb. I'm sure the comments others have provided are valid, but time has shown the system as described has worked reliably and trouble free for me. There's always room for improvement. Take what you like and leave the rest, your mileage may vary...