Here are some free Sewer Tiles. Each tile is 4"x 4" (two per page) so you can build out a simple fantasy sewer tunnel.
I figured it would just be easier to draw them out on the Paizo Battlemat but it is such a simplistic design that a simple line drawing isn't very evocative.
So there is some free stuff. By the way I wish someone would comment. I'm working in a vacuum here. I'd like to know if anyone is having trouble with downloading now that it's on Google Drive.