On this page of the game guide to Borderlands 2 you will find a detailed description of the side mission titled Capture the Flags. You can start this quest in the Sanctuary location after completing the main mission named Where Angels Fear to Tread.
3) Bandit camp/Generator
4) Tunnel entrance
5) Tunnel exit
6) Generator 2
7) Bandit camp 2
8) Generator 3
Brick  will give you a mission of capturing three flags of the rival gang. Use Fast Travel and move to Sawtooth Cauldron. If you haven't yet activated the device, head to The Dust and to Eridium Blight through the passage in the west. In Eridium Blight, in the north-east part of the map, you will find a passage to Sawtooth Cauldron. When you get to the right place, head down into the camp below  by following the path marked as . There you will find the device from the above screenshot. Place the flag in the marked spot and Use the lever on the generator.
The flag will start raising and you will have to protect the generator from incoming Bandits. If the generator gets damaged, Use the lever once again. If you don't kill enemies in a given group, the next one won't appear. Therefore it's worth to keep a single Bandit alive and avoid his attacks. With the flag raised, destroy the generator.
Go through the underground passage number  (entrance) and  (exit). Run to the next generator , place the flag and turn on the power. Once again you will have to fight off the Bandits (including airborne ones). You can retreat to a safe distance and assuming everything goes right, the Bandits will be busy with the local Threshers and not the generator. Remember about turning the power back on should the generator get damaged and stop raising the flag. With the flag raised, destroy the generator.
The last flag has to be placed in the north-west part of the map . You can get there through the camp marked as . Beside the generator, you have to repeat the whole process with placing the flag on the top. When you're done with that, destroy the generator. Return to Brick  in Sanctuary and collect the prize.