Rain Harvesting Water First Flush Downpipe Divertor Kit protect your rainwater quality by diverting the most contaminated water that washes off your roof with the first few millimeters of rainfall with a first flush diverter. This First Flush Diverter is the original in our range and is a great way to get started with the first flush diversion. This improves the quality of the rainwater you collect and is a key step in effective Rain Harvesting practices. Divert the most contaminated water that washes off your roof to give you the best water in your tank.