I use a 5-gallon bucket I picked up from Firehouse Subs (Their famous pickle bucket). I had to clean it out and let it sit outside to let the pickle smell dissipate, but it works well as I only keep enough on hand to top off my tanks plus a few other uses around the house. If you are only keeping small amounts any bucket made from food grade plastic will work. You can get them at restaurants, restaurant supply stores and even your local home repair store like Lowe's or Home Depot.
Why do I love fish? Because every time I stare into the little world I have created for them, every problem I have just floats away....