The Empty Garbage Task consists of 2 stages. The first stage is located in the Cafeteria Room, all you have to do is pull and hold the lever down until the garbage has been emptied.
Once the first stage is done, you have to go down to the Storage Room and once again pull and hold the lever down until the trash is empty. Keep in mind that this stage of the task is Visual and once the task has been completed, players can see the door outside the ship open and release all the trash out. If you watch a person do this task, it means they are a confirmed crewmate since imposters can not fake this task.