From the starting location, in Liberty City, go north on the starting road past the park, all the way until you get to the Beast, then go north on that road, around the bend until you get to the next major 3-way intersection. Take an immediate left on that major road. Go over the bridge and take a right on the road, heading north, immediately after it. Go past the Hospital and Police station, then take a left on that major road. Follow that road until you get to a 3-way intersection with a 6-lane road. It is the first sewer on YOUR right. Get out of your car and step on the curb next to the sewer, you should fall through