I was an old school engine oil changer so far, because I was sure that only the old oil can be completely out of the engine. Through some contributions here I became curious and got me a mechanical pump with 9 liters volume. As a result I got a little fuzzy, so actually the whole oil can suck off from the engine. My neighbor of the car locker of the old guard is, said that you should drain all 2 suctions once. What do you think of this procedure? Or something?