Some get through, my TDS is 30 before I flush, I wait till it’s reading 2 before closing the flush valve.
Yes but the flush valve does not remove the TDS creep on the permeate side. Depending on how long it sits inactive but if it sits long enough the TDS will equalize on both side of the membrane. The flush valve is on the feed side of the membrane so the lowest the TDS can get is that of your feed water.
@Buckeye Hydro has a FAQ on his sponsor forum