did you get the suspension control from him (the remote that raises the car up and down)? Is he currently on top of where the sproutella was original spilled or is he near the headquaters of the resistance?
And by sewer, do you mean that big dark tunnel at the end of the sewer that Manny won't go in because it's dark? From what I remember Manny wants to use the headlights on the Bonewagon to illuminate it. Once you get the remote and make the trail with the grinder Glottis should drive their automatically.