Flush Valve Assembly for Reverse Osmosis Systems The correct flow restrictor required for your RO system depends upon the capacity of the membrane.Please see the table in the description below for estimated examples. Variation listing allows you to choose the correct sized flow restrictor required for your system. Flush Valve Assembly for Reverse Osmosis Systems This is an attachment that can be added onto the waste/drain line of a Reverse Osmosis System (Aquarium or Domestic) which allows water to bypass the flow restrictor. This then allows the build-up of pressure within the membrane housing to be released, subsequently allowing water to run across the surface of the membrane to flush it. This attachment is handy for customers who may have a compact reverse osmosis system that doesn't come with a flush valve as standard.