Save water with a more efficient method.  Add a second membrane to the waste line of the first membrane to decrease waste water and produce more pure water.  This kit includes:

• Membrane housing with fittings
• 100 (or 150gpd) membrane
• Additional blue tubing
• 6' black waste line tubing
• Y-connection to combine both pure water lines before the DI stage
• Two C-clamps to affix housings to each other

Caveat: By adding a second membrane, pressure will drop accordingly.  If you discover your water pressure isn't going to be enough for this upgrade, you may want to add a booster pump to bring the feed to 60 PSI for better results.  Booster pump kit 
Add a Pressure Gauge too. 

Installation Procedure:

1) Remove waste line from current membrane housing. It's the black tubing.
2) Locate and remove the flow restrictor and set this aside. It is inserted in the tip of the black tubing you removed. Don't lose it.
3) Affix new membrane housing to old membrane housing.
4) Cut the black waste tubing previously removed to the proper length necessary and install one end into the old membrane housing and into the intake of the new housing.
5) Affix a short piece of blue tubing to the output of the new housing.  
6) Insert the flow restrictor in the new black tubing included in the kit, and install that into the waste line port of the new membrane housing. This flow restrictor will create the correct back pressure for both membranes.  It MUST be installed on the secondary membrane housing.
7) Lead the two blue lines (good RO water) and cut where desired to install the Y-connection.  Then insert more blue tubing from the Y-connection's single end to the white square ASOV's (auto shut off valve) IN side.
8) Point the black waste line to a nearby drain. Turn on the system and test for leaks.
9) You're done!  Enjoy better production and less waste water.

Video how it all looks when assembled properly: https://youtu.be/3ndETueo5CA