No manual, but the way I do it is to push the mouth of the vacuum tube a couple of inches down into the gravel. The gravel will start to swirl and will go up the tube a little bit. Then you'll see all the dirt coming out and this will get syphoned away, but the gravel won't actually go anywhere. Push the tube up an down a little bit to stir things up a little. Once the water runs clear slowly lift the tube out of the gravel, and all the gravel in the tube will fall back down where it was. Move the tube a couple of inches over and repeat! And also if you can lift up rocks and wood every now and again, you won't believe how much mess gets under those things!
HTH
Sarah