[pikeman]

Going to fit new membranes. Just wondered do you need to flush them out

[Don Kee]

Yes

[Frankybadboy]

no 

[Ian Lancaster]

I would, well - maybe I wouldn't, but I might - then again I might not - go for it, can't do any harm - on the other hand it would waste water...........

Seriously, by the time you've run water through the system to check for leaks you've probably done all the flushing that's necessary.  To start the TDS may not be very low, but after it's run for an hour or so it should come down to a reasonable level.  We changed one a month or so ago (300gpd) at first was showing 22ppm from 320 input but within 15 minutes was down to 3ppm

[slap bash]

A new membrane being new will contain nothing to hinder the pure process.  So  the answer is NO.

[Perfect Windows]

Going to fit new membranes. Just wondered do you need to flush them out

According to June at Gaps (whom I trust totally), yes.  She says they are soaked in preservative.  She reckons 20 mins to half an hour.

Vin

[Dave Willis]

What he says ^  when you open the bag it's got a slimy coating inside.