You make some good points.
When changing oil you will do a better job if the engine is hot. At that time the contaminants are mostly churned up and suspended in the oil. Also the oil flows better thus more of it comes out. The dirty oil left behind when doing a quick oil change, whether with the drain plug or the topsider, is the oil clinging to everything above the bottom of the pan. It takes awhile for this oil to make it to the bottom of the pan.
I would suggest that with your method, you could do a more thorough oil change by; doing your 15 minute "suck" shortly after turning off the hot engine, and then do another 15 minute suck the next morning after it sits all night. The last oil to find it's way down to the pan is the dirtiest, sludgiest in the engine. That's where you really get a thorough cleaning effect. It would seem to me this would be a great way to get the best of both worlds, the convenience of a topsider along with a more thorough cleaning of the engines internals.
Change oil hot and change oil often,
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
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