Yesterday my students and I in Envisaj, the Mercy College Environmental Sustainability and Justice League (club),  built our second DIY Solar Hot Water system using half size (500 mm long)  vacuum tubes from http://www.electric-bike-kit.com/solar-tubes.aspx. 

This time we used a 4" inch fence post with 10 2" uniseals to seat the vacuum tubes.

Here is a picture of the progress we've made:

Is anybody else out there working with solar vacuum tubes to make their own heaters?  We'd love to share ideas with you (sucesses and failures!).