Gas-Guzzing Rakks include this Slagged Rakk in Borderlands 2

In the mission Gas Guzzlers from the Mister Torgue's Campaign of Carnage DLC, Sir Hammerlock sends you to investigate some Rakks in the Southern Raceway and collect their Gas Sacs

The Gas Guzzing Rakk include:

Slagged Rakk

Chubby Rakk