The Hydrotech 33139 Retrofit Kit is for the 101 Series, 102 Series, 103 Series, 1010 Series, 1020 Series, and 1030 Series RO Systems. When replacing the flow control, you only need to install the Hydrotech 33139 Retrofit Kit the first time (unless the 33139 breaks). After installing the Retrofit Kit, it is recommended you replace the 40600042 Flow Restrictor piece every time you replace the RO membrane. This retrofit kit updates the drain line flow control to the type used with the current Hydrotech Reverse Osmosis Systems (1240 Series). This retrofit kit includes an internal plug assembly for the manifold and a capillary flow control contained within the red drain line tubing.