I've used a roasting pan for a horizontal quench tank. It was of rather heavy guage metal. I don't do much edge quenching any more, but that could change, and use a turkey frier for a vertical quench tank. I have also JB Welded some 1 gallon paint cans together for a quench tank. The interior rims at the mouths give ridgidity to the assembley but they are a little tricky to get lined up. The ends can be cut out with a can opener. I smeared plenty of JB Weld over where the ends were glued together to make sure there weren't any leaks.
Doug Lester