GAC will come out of the drain line if the carbon has not been allowed to soak for a day or two minimum. Most GAC manufacturers recommend a 72 hour soaking. You can speed up the start up by putting the valve into fast rinse (rapid rinse) and allow it to run in a downflow for an hour to the drain or you can even water your lawn with it. Do not let this water get into fish ponds, some GAC's will have a considerable affect on the waters pH for the first few weeks which can affect aquatic life.
Did the system come with a top screen? What DLFC button do you have? What is your water temperature? What size system?
If you want to try it again, put the unit into backwash with the water turned off. Crack the inlet valve and allow water and air to exit the drain very slowly for an hour or so. Then do a a rapid rinse for an hour. Open the water line all the way and retry.
This should get you started, but please answer the questions above so we can make sure your system is set up correctly.