An essential supply for a fish tank keeper is a bucket. The bucket should only be used for your fish. That means don't go mopping your floors and using your fish bucket to keep the water in.
It's nice to have a fish bucket in your arsenal of fish tank supplies. It can be used to hold your other tank supplies, transport fish, acclimate them, and use it to add water to your aquarium.
I recently used this handy supply to acclimate my new Crowntail Betta. He needed to get used to the water before putting him in his fish tank and installing it.
A fish supply bucket should be in every serious fish keepers supply list.
Never ever use your fish supply bucket for anything else than your fish tank maintenance. Ever. Ok, I've probably made that clear. Obviously you will be setting up, or have set up an environment for your fish that is stable. You don't want to kill them by introducing something foreign they might not like. Like detergent!
I've marked the outside of my bucket, FISH ONLY. I'd advise doing the same, and storing it with your other fish tank supplies.