Here's the recipe for big, gorgeous bubbles that don't pop easily. I quadrupled it to have enough for the galvanized tub.
1 gallon distilled water
2/3 c. Dawn dish soap
2 T. glycerin (I found some at CVS)
Mix together. You can make bubbles by bending pipe cleaners into fun shapes, or try cookie cutters. For big bubbles, slip two straws onto a long piece of strong and tie the ends together. Use the straws as handles. I've also seen metal hangers bent into a circle, but that sounds a little dangerous.