Downspout T-Adaptor - Inline Downspout Cleanout - Elbows
If you wish to add optional first flush capability to your downspout diverter, a downspout T-Adaptor with an appropriately sized bottom extension connected will do the job. First flush routes the first flow of rain water away from your rain barrel or water storage tank and eliminates much of the contaminants lying on your roof such as dust, dirt, pollen, insects, residues, bird and rodent droppings. Larger debris should be filtered by a combination of gutter screens, downspout strainers and a downspout cleanout located upstream (higher) from the diverter. The downspout cleanout either box or inline types, allows you to more easily empty out filtered debris and minimized servicing of your T-Adaptor's first flush extension or standpipe. The T-Adaptor extension will be capped on the bottom and have very small (pin-hole) drain holes near the bottom which allows the water to gradually drain out, perhaps routed over to a planted area. During a rain shower the bottom portion of the T-pipe extension will first fill with the rain water until the level reaches the horizontal outlet then subsequent rain water will exit the T-adaptor and drain into your water tank or rain barrel. Recommended first flush rain water diversion is at least a gallon of water per 100 square feet of rain collection area. For example: say you are using 4 inch round downspout pipe, then you would need a 18 inch length of extension pipe per gallon while 6 inch downspout pipe only requires about 8 inches extension length to hold a gallon. If your one downspout services say 400 sq feet of roof area, the first flush T-adaptor extension would need to be 32 inches in length using 6 inch diameter pipe or 72 inches (12 feet) in length using 4 inch round downspout pipe. Depending on how often it rains, amount of debris accumulation and how well you filter out debris and sediment upstream, you will need to occasionally remove the bottom cap of your first flush extension, to clean out accumulated debis or residual sediment to keep the bottom drain hole open and unobstructed. The pinhole drain hole(s) should be located higher than absolute bottom of the capped extension to prevent residual sediment from quickly clogging the small drain hole(s).