I would disconnect the tubing from the pre-filters and run that for a few minutes to help wash out any carbon dust etc. from the pre-filters. Then I'd hook the line into the RO membrane and disconnect the tubing to the DI. If you have a flush kit or valve to control waste water, run that completely open for a few minutes. If not, don't worry about it. If you have them, run them wide open for five or ten minutes and then pull it back to a normal 4:1 ratio of waste water to output water. Run water through the membrane for an hour or two, and then connect it back to the DI. Make a few gallons of water with the RO/DI and discard it. Then you can start using the RO/DI water in your tank. It's always best to flush everything out, just in case there are any manufacturing residues etc. that need to wash out of anything, which would keep your initial water from being completely pure.
-Joe