From the Commonlands, enter the Thieves' Way. Take the South Freeport sewer grate to zone into Freeport.
Avoid guards as you make your way to The Militia Recruiting Center, a clickable trapdoor next to 2 Freedom Road ( -160, -34, 150 ) /waypoint -160, -34, 150.
Once inside, do NOT move (unless the mobs are greyed out, if so ignore this step)! Hail the Freeport trooper at the counter from where you stand. Tell him 'Here you go' when he asks for a pass. The militia troopers will not aggro now so okay to enter the room.
Take the door to the the north (or the left door way), which leads to a bunk room.
Behind the bookcases there is an even-level, single up arrow Militia Captain. Right click and HAIL the Militia Captain. He will attack no matter which answer you give. Now run out of the room, make a left and run up the steps, training all the guards behind you (You don't need to kill the Militia Captain). Make a right into the outdoor area and head towards a palm tree which is clickable and zones you out to the front of the basement.
Exit Freeport using either the marine bell by the docks, or the Thieves' Way, and return to Gil McMartin. If you die, you will automatically revive at the front gate in the Commonlands.
If you do inadvertently aggro the mobs in the zone and they kill you, you will respawn outside the door. You can zone in, run up to the roof where the tree is, and click on it to complete the quest (providing you have already talked to the Militia captain.)
Note: This is the easiest of the Loyalty Quests. Furthermore, it is repeatable if you keep declining the other quests From the Loyalty line from Gil McMartin, he will eventually offer it again.