5 years back when I installed my solar hot water you could not install a drain back system when using ecauated tubes. The evacuated tubes could be damaged if they sat out in the sun without the heat being taken away from them. Recently someone told me they have new tubes that can be used with drain back solar systems. Hvae any of you used them or know of them? Do you have any links that would help me find them? Thank you for any help you can give me.