Dexter wants the potion recipe that Kor Kalom uses. If you want to join the Old camp (or just want the XP) accept the quest and then ask Baal Pervez (usually standing just next to Dexter) to take you to the camp. Make sure you keep pace with him; if he gets too far out of sight he will go to the camp without you. Once you get to the camp, follow the left path over to the big courtyard. Facing out from there, take the leftmost path. It should lead you under a bridge and past a small shop. Find the nearest ladder and climb to the upper area. You should now be by a hut that has "Kalom's Bodyguard" standing outside it. Go on in. If you want to you can ask Kor Kalom to sell you the recipe, but he will refuse. You can't steal the recipe while Caine is there, so wait until he leaves for the night. As soon as he is safely out of sight pick the lock on the left chest (Kalom won't notice you doing this). Bring the recipe back to Dexter and he will reward you. He will also give you his vote for Admission to the Old Camp.
Because nobody saw you take the recipe, doing this quest does not prevent you joining the Sect Camp at a later date.