Allow any stains or paint on the canvas drop cloth to dry.
Beat the canvas cloth against the ground to remove caked-on paint.
Spray the canvas with a homemade or store-bought canvas cleaning spray. You can use a mixture of 1 part mild detergent or vinegar to 3 parts water.
Scrub using a small brush, and soak the canvas in warm water.
Add powdered or liquid laundry detergent to the water. Try using enough detergent for a small load of laundry.
If stains persist, you can run the canvas through the washing machine on the gentle cycle. Use warm water and a mild detergent.
Allow the canvas to air-dry to avoid unnecessary damage.