pppshaw...
Flush kits are optional and their effectiveness is questionable. I never flush my membrane and I'm doing just fine.
And yes, you are supposed to keep the membrane moist. It doesn't have to be submerged, but it should not be allowed to dry out. Usually just keeping it in the chamber, even if the water is drained out, will keep it most enough. Most people have their RODI system permanently deployed, they don't just bust it out when they need to make water, so this isn't an issue. You may want to think about doing the same.