The Exterminator Quest

Go to Padreia in Carlins Druid guild, here. Ask her about a mission. Your Quest Log should update and you will receive an special flask.

Go to the sewer gate, hereand go down, walk south and be prepared to fight some Slimes. Go down another floor and fight more Slimes. Finally use the poison flask on the water, this will prompt to update your Quest Log.

Go back to Padreia to claim your reward.