*Volume Discounts Available* US Patent Number: 8,113,220 B2: The Original Concrete Washout Bag. EnviroSac Waterproof Pump Bags utilize a more effective and adaptable design that helps simplify the concrete washout system. 40% stronger than the other brands; these Pump Bags fit under all hoppers and feature a rugged design, which makes the bag the most durable and reliable bag on the market. The bag has a waterproof liner and holds 1.3 cubic yards. Straps allow for easy transport even before the concrete has fully set up.