Hi Mark. Guess thats where mine is also, as I have the flush valve on mine. This unit has a Santi-Purge valve on it, which I guess is similar but not the same as it allows water in the system to purge it with chlorine.
http://www.waterite.com/main.html
So the inline restrictor must be needed then. I wonder if it matters which end of the waste line its in. Inst. said on the drain pipe end but I think we have it on the membrane outlet end. Cant see it being directional just a restriction?
Geez, all the others I have put in are simple to use.