Looking around to see what I have on hand and see a old 100 gallon l.p. tank wondering if it would work. I'm new to this kind of thinking but handy at building once I have the idea in my head
That should work just fine for a 6" or 8" system. Plenty of people have described using them before.
You will just need to make the insulation on the heat riser good enough without being too thick, so as not to choke the downward gas flow between inside of tank and outside of riser.
Be sure to investigate safe methods of cutting the tank; you want to get the valve off and fill the tank with water before cutting, to minimize the possibility of residual gas exploding.
