This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
A mop wringer may be made and attached to an ordinary pail in the following manner: Two pieces of metal, A, are attached securely at opposite sides of the edge of the pail, holes being drilled in their upper ends to serve as bearings for the roller B. The piece of metal C, which is duplicated at the opposite side of the pail, is pivoted on a bolt. These pieces also carry a roller, E, at their upper ends and have a crosspiece,F , at their lower ends. Discarded wringer rollers can be used for B and E. A coil spring is attached as shown, to keep the rollers separate and in a position to receive the mop. When the mop is placed between the rollers they are brought together by a pressure of the foot on the crosspiece F. - Contributed by J. Dennis McKennon, New Britain, Conn.