The rinse-water bucket is an indispensable tool in the cleaning arsenal. To make cleaning less of a drag — and a mess — use a 10-quart, square plastic bucket. The size minimizes weight so that most people can easily carry a filled bucket; the shape helps prevent sloshing and spilling; and the plastic won’t rust, scratch or dent. Choose a bright color to reduce the chance that someone will fail to see it and trip over it.
For many cleaning jobs, try using two buckets — one to wring dirty cleaning solution out of sponges, cloths or mops, the other for soaking up clean detergent solution. To test for sufficient cleanliness, drop a quarter into the rinse-water bucket. When you can no longer see the coin at the bottom, the water has become too dirty for further rinsing.
Reference:
Don Aslett in The Cleaning Encyclopedia: Your A to Z Illustrated Guide to Cleaning Like the Pros.