Destroy dark eco tanks is a mission in Jak 3. Ashelin Praxis has somehow gotten word of the Metal Heads storing dark eco in caches in their city section to create dark eco weapons to infect the city. With Jak inside the district she told him to go and take out these caches.
The PlayStation 3 and Vita versions of this mission are related to a trophy named "Tanks for the Mammaries", completing this mission will reward you with a bronze trophy.
Primarily a JET-Board mission while you go through the Metal Head city district, which is infested with stingers and grunts. They're not a real problem but watch your back whenever you are on the sidewalks. For starters get on the jet board and grind on the purple cable here, then jump up to the first dark eco tank and destroy it. Take the next cable and you will see a strange plant that sometimes emits a burst of air, so stand on it and you'll be launched to another platform.
The majority of this mission pretty much consists of grinding over the purple cables (some of them have an electrified knob in the middle), using the plants to get around as you go through this district. After destroying the fourth tank the nearby plant launches you into the acidic pool in the center here, where you safely land on some sort of hard growth. Cross through here until you reach another plant and use it to reach the fifth tank.
Upon its destruction a sixth one is revealed next to the strange Metal Head barrier blocking the route to the Port. Destroy it and start a cutscene, afterwards use Jak's new Dark Strike power to break open the aforementioned barrier. After this you will automatically start the next mission: "Kill dark plants in forest".