Not sure how much of a trick this is actually, but makes it a bit easier.
When you descend into the sewer part, there are 3 large mobs that are fairly tough. If you pull the lever to send the lift back up it creates a square in the middle of the room that you can fall through. When you pull the mobs, retreat to this room and just circle around the square. Eventually the mobs will do a tail swipe that will send them to their deaths.