OK first shoot the barrels out on 3 of them to destroy them easily. Then hop in the bulldozer and run over the people as you work. You have to get a running start to hurt the last three. The firetrucks show up quickly to put out your fires. Be sure to watch out for the orange barrels, which are explosive. They are super nasty and can take out your entire bulldozer and you too.

Now for the fun. The foreman is hiding in the toilet. Go push the toilet with your bulldozer until it falls into the rectangular hole over by the light. Make sure it is the MARKED toilet and not just any one. Then go to the cement mixer and pour cement into the hole. There isn't a timer ticking, but if you take too long you will fail the mission.

After you get the cement mixer to the red spot, it dumps in the cement and you get

Mission passed!

Cesar calls and talks about the drugs again. You get another call - Jethro talks to you about your car destruction. He has an advanced driving school to teach you some moves.

Grand Theft Auto San Andreas Walkthrough