Go to the construction yard near San Fierro. Go past the crane and turn left after the first hangar. Behind that, you will see a towtruck, Get in and drive towards the Bulldozer. Hook up the Bull Dozer. Drive up the hill to where there is an open area. Then, turn very sharp to either the left or the right. The Bulldozer will fling around, pulling the tow truck with it. For even more fun, get three or more tow trucks and hook them all up into a line. With three or more, the Bulldozer acts like a ball and chain flailing around.