Our rain barrels come with a single overflow but if you want increased flow or want to connect your rain barrels together then you should grab one of these extra overflow valves. Made out of solid brass these are built to last and you just have to drill a single hole and use a wrench to screw it on, easy as 1, 2, 3. No adhesives,  silicone or extra hardware required. These have two thread one is NPT and the other is Garden Hose standard thread.