I love getting free tanks.
Durring the summer I picked up a 60 gal and a 30 gal from a family friend. We also have these sort of junk exchange things in my area where each neihbourhood has a time period to put out unwanted junk then the city comes and cleans it up. Most people put it out early and much sofa/tv/chair/rug/ect. claiming happens. I gathered 2 20gal tanks and a hexogone tank (I think it's arounda 30gal.
Whew - so many more tnaks then pets, but you never know when you'll need a new one!