Jim - I've done a form of "mud jacking" with an old style tire hand pump. The cylinder was about 1" in diameter and the top cap was held in by two screws and could be removed. My driveway had settled on a corner of one section. First I drilled a hole in the low area, then filled the tire pump with a very thin cement/water mix, inserted the hose in the hole (make sure the hole-to-hose diameter is a tight fit) and forced the mix to flow between the slab and the dirt. The pressure (pounds per square inch) that is created is high compared to the weight of the concrete and the slab will come up. (A 1" cylinder with 175 lb. of force applied will result in 175 psi pressure.) If your slab is still level, you can just pump the mix into the void and it will set-up.