I got my buckets from the dollar store. I mix my water in the blue one, and put my old water/rinse off my filter in the white one. They're only used for the tank.
When I first got my tank, I didn't have a heater for the water changes. I would just put the bucket in the sink with a thermometer freely floating, and fill the sink with hot water (making sure no nasty tap water got in the bucket). Eventually the water in the bucket would reach the same temp as the water in the tank. So if you're ever stuck without a heater, there ya go. My heater for my water changes shorted out last week, so I had to revert to that method again.