When you fight the Sewer Bot, he uses two attacks. He hits a cannon and fires one or two sewer water balls; and fires one or two robot dogs from a separate cannon. After the Sewer Bot has shot from all, or a few cannons, he will have to reactivate them. However, Rodney's cannons reactivate automatically after awhile. When the sewer bot is running to a cannon to shoot it, hit the cannon facing that cannon and hit it a few seconds earlier. Othwerwise, he will move away to another cannon if you shoot it too late, and he will not have gotten there yet and the sewer water ball will hit the ground. Time it correctly for him to get hit. He will usually fire a few robot dogs over to destroy you if you hit him. Keep hitting him the same way a few more times and he should be defeated.