If you paint with water color or acrylic paints, you will need to clean out your brush when changing colors. I find the water buckets the art stores offer, too small. For acrylics, I'd rather use a bigger container. I like this bucket because it has handles which makes it easier to transport to the studio.
Simply take a sponge holder (from the sink), flip it over and suction cup to the inside of the bucket. Your sink will never miss it! And now you can work the paint out of the brush or keep your brush moist when not in use.