An over flow pipe for you water tank is a step but a Mozzie stopper high-flow flap valve is the ultimate step to improving your rain collection experience. Be sure not to over rotate or leave open, as doing this will prevent the mozzie stopper from working correctly and doing it's job of keeping out mosquito, birds or small critters that will scurry to the overflow pipe. A clean tank means clean higher quality water. Another feature that contributes to the water quality is the ventilated flap valves allowing movement of air across the water and preventing a vacuum formation which can break the system when dealing with large quantities of water. Available in 3 and 4 inch.