Its in bowerstone industrial, across from the orphanage. From where you first enter bowerstone on the quest where youre going yo meet the rebels for the frist time, cross the river and keep going untill you come to a three way intersection. In front is a big stone gate with the reaver industries sign, and to the right is a road with a bunch of houses on the left, and the orphanage on the right. The orphanage is the big building behind the broken down fence. As far as I know, the only way I could get into the cesspools was doing the quest where Laszlo's wife gets kidnaped. The entrance to the cesspools is in the third house from the bridge to the right, its across from the orphanage.