Just wondering if it has been done, Has anyone out there built a large tank out of steel, i've seen plywood tanks, but never out of steel, i know it can be done with stainless but i have a lot of spare sheet metal and just wondering, not worried about support, i've built holding tanks for waste water for people around here more than a few times and they are normally 8'x4'x4' and some 8'x8'x4' and they hold fine for years on end with very little flex while full.