Any flood prevention strategy has at its core, a device known as a backwater valve. This device allows wastewater to only flow in one direction. If the sewers become overwhelmed this valve closes preventing basement or crawl space flooding. We at PBF Plumbing use only the highest quality Canadian made and city approved (normally open) backwater valves from mainline. The device is usually installed at the last clean-out in the basement and generally replaces the existing building trap found in most older homes.