Wow, it's been awhile! Glad to see you post! Assuming you are referring to the seam on a metal tank, good old solder does the trick. Liquid flux in the seam, and even lower melting 60/40 will work. Let it flow, wipe with a wet rag. Use a wet rag as well to heat sink areas you don't want to melt solder at. Use a propane torch, you don't need much heat, and you don't want it over a large area.