The flow restrictor will go on the waste water side of the membrane housing
(the horizontal thing on top of the Prefilter Cannisters) The Waste water line
is on the side that has two outputs, the waste water one is usually offset
while the filtered water one is centered.

You can also go he
http://www.simplydiscus.com/forum/in...isplay;threadi
d=7886
For a close up look at the different components that make up an RO unit, Feel
free to ask any questions you might have. I'm sure I can help you.