Guard your home against unwanted basement flooding and sewage backup with the Sentinel Drain Guard Sewer Backflow Preventer Model DG100. This highly innovative, inexpensive backwater valve is designed to fit standard 3-inch and 4-inch floor drains using an included adapter. Crafted from durable ABS plastic with premium silicone gaskets and O-rings, the mechanism sits in a normally open position to permit regular wastewater drainage but closes instantly to block rising sewage during heavy municipal grid overloads. It requires zero active maintenance after setup, installs easily in just one simple step without requiring plumbing modifications, and comes complete with a fitted drain cover grid. This specific item is in used-fair condition, which means it may show visible external scuffs, scratches, or signs of previous handling while retaining its foundational structural integrity. Perfect for urban homeowners seeking a dependable, CSA-certified, and Holmes-approved DIY solution to secure their lower levels from messy overflows