How can I stop a stainless steel drinking water tank from leaking?
I would suggest using a product called "Sealsall". You can get it at any hardware store.  This stuff is easy to use, Dry the seam as best as you can, then just apply some to the leaking seam before it gets too wet again. Try not to get it on your fingers as it will take a week to get it off!!  Sealsall dries clear and should be good for years.  I have used it on everything from a canoe bottom, car gas tank, to hot tubs with success.  Good Luck