Remove drop cloth from the package and cut down the center seam.
Put one half of the drop cloth loosely in a top loading washing machine. (Wash the two halves separately so the bleach can be more evenly distributed and not overload the machine.)
Set washer to hottest setting and let the machine fill with water. Pause the machine.
Measure 8 cups of bleach and pour into the washer. (I dilute my bleach with water in a pitcher. To do this, I add 2 cups of bleach at a time to a plastic pitcher and then top it off with hot water. Then I add this to the machine around the drop cloth. Repeat until all 8 cups of bleach have been added to the machine.) Note: If I have less time, I add 10 cups of bleach to the water and shorten the soaking time to about 2 hours.
Un-pause the machine and let it agitate for a minute to mix the bleach into the water. Then pause the machine again and set a timer for 1 hour. After 1 hour, un-pause machine and let it agitate for a minute and then pause it again for another hour. Repeat this cycle for a total of 4 hours. Make sure all the fabric is submerged in the water, using a long-handled plastic spoon to push the fabric under the water.
After 4 hours, un-pause the machine and let it continue the wash cycle.
Start the machine again and wash the drop cloth with detergent and white vinegar in the rinse cup. Repeat again on another wash cycle with detergent and vinegar to get all the bleach out.
Dry thoroughly in a dryer to preshrink fabric.