I use a 1500 psi pressure washer. Stick the end of the washer nozzle in the oil fill tube and blast away till clear water runs out the drain. To get all the old oil out I do this while the engine is running. Now you may ask, "How do you get all the moisture out?" Well, thats the easy part. I just take off the filler cap and leave the drain plug off and run the engine till it all dries up. If my oil is really dirty, I throw in a cup of Tide detergent (with bleach).
The pressure washer is also good for cleaning out brake and fuel lines, and really works getting dirt and dust out of hard to reach areas around the dash.