The overflow box effectively transport aquarium water to under cabinet sumps, refugiums, or wet/dry filters. These high quality overflow boxes features bulkhead fittings for secure and convenient installation. The U-tube style compact overflow boxes are designed to fit between your tank and your wall to maximize space usage in your aquarium setup. With only 3 in. required between your tank and your wall, these boxes are excellent for optimizing space. Each box includes everything required to attach it to your system.