The dark eco canister is a Precursor artifact found on Misty Island during The Precursor Legacy, and later in Haven City during Jak II and Jak 3. It is a small canister made of Precursor metal containing dark eco, and has the hazard mark for dark eco on either side transcribed with Precursor writing reading "beware" around the device.
Daxter tripped over one of these when he and Jak were exploring Misty Island, however only Jak was able to activate it. Shortly afterward, they were attacked by a bone armor lurker. Jak hurled the canister at the lurker, the resulting explosion killing the lurker and knocking Jak into Daxter, who fell into the dark eco silo behind him.
Dark eco canisters later appeared in Jak II in a much smaller form as the shells for the guard grenade launcher. In Jak 3, they appeared again in the mission "Hijack eco vehicle", during which several dark eco canisters could be found on the cargo transport which Jak stole from the KG Death Bots. Ashelin Praxis, who assigned the mission, mentioned that they were used to store eco, which if stolen could prove highly valuable as supplies for the war effort.