Get cleaner rainwater into your tank. Between downpours, dust, leaves and animal droppings can settle on your roof. When the rain returns, the first flush of water washes them off, and your first flush diverter sets it aside to keep it out of your tank. So only the cleaner water that follows is stored. Its patented Catch-All Tee captures more of that first flush than a basic tee, so even less makes it through to your water. A great step up from the Basic Tee.