I've never used sonotubes before, but where I live now the building code is recommending a sonotube or like product for the footings of my deck. Frost line is 36 inches so I was planning on digging my hole 48 inches and putting 6 inches or so of rock down first and then the concrete on top.
However, I have seen or read several different opinions on how to install the tubes and by building code office is really giving me anything on how to use them. Place a tube all the way to the bottom of the hole. Place the tube only a foot or so down from grade and fill with concrete. In the second case concrete would be contacting dirt for the bottom 30 inches and then sonotube for the top 12 inches.
What is the preferred method for installing a sonotube? Is there a better method I have missed?