The ABS 2"Double Ell Tapped is used to divide the flow of greywater into two equal sections in a branched drain system. The double ell should be placed on a brick or stone and leveled so its perfectly flat. To get an equal split, you need a straight run of at least 2 feet entering the fitting, if you don't have this distance the water may not be equally divided. Typically a 2" double ell is only used in the first split, 1.5" double ells are used after that since there is less water.
The cap can be removed for cleaning out the system in case of clogging. This fitting should be located in an accessible spot, like inside of a valve box.