How about as a tool for an individual to do "in-between" oil changes themselves? I have seen some private-use models advertised with a 6.5 liter capacity. Is that enough to drain say a 92 500E (or most other MB models) in one sitting? Do you feel there are any advantages to sucking out the oil through the dipstick tube or draining it from the bottom of the pan? (aside from the inspection thing) I've heard the old tale of how the drainage method removes all the sludge, how the plug is magnetic and gets the metal shavings, etc. How much validity is there to that tale regarding MB? Do you recommend any particular model for this application?