To maintain some degree of efficiency, there has been a trend to specify larger traps. Unfortunately, providing a large tank for the effluent to stand also means that food waste has time to settle to the bottom of the tank, reducing available volume and adding to clean-out problems. Also, rotting food contained within an interceptor breaks down, producing toxic waste (such as sulfur gases) - hydrogen sulfide combines with the water present to create sulfuric acid. This attacks mild steel and concrete materials, resulting in "rot out", On the other hand, polyethylene has acid-resisting properties. A larger interceptor is not a better interceptor. In most cases, multiple interceptors in series will separate grease much better.