In the event that your rainwater tank is full and additional rain continues to enter, the system would back up. Therefore, a tank overflow outlet pipe of equal or greater volume than any inlet pipe(s), is used to discharge overflow stormwater to grade, storm sewer system, or in some cases to a seep away pit underground.
The angled skimming overflow pipe inside the tank will remove floating debris from the water surface. Only small floating debris such as pollen can make its way past the pre-filter.
A backflow preventer device is used to prevent backup of water, as well as unwanted debris and rodents from entering the rainwater tank.