18. With the corners tacked together, John places tack-welds every 4 inches along all the seams then welds each seam in a single continues bead, stopping only when more rod is needed. Welding a tank is different than welding sheetmetal, where warping is a constant battle. Most leaks in a welded joint occur when one weld bead joins another, so the fewer stops and starts the better. The thick material will resist warping.