i do my services first thing in the morning AFTER all the oil has settled, so i know i have removed as much of the old oil as possible!
i dont understand why people do an oil change when the car is hot... i thought that was a thing of yesteryear when oil pumps were weak and unreliable! and if they sucked up air they couldnt "self prime"
I guess it is an old thing. The theory is that when the oil is hot it will flow out quickly and flush out the sludge from the pan with it. There is unlikely to be sludge these days and that fact makes me confident that not draining at all is still satisfactory.
For the reason you mentioned I also change the oil when cold to allow as much as possible to drain to the sump but this is probably a mythical advantage. Changing 90% of the oil is (in practice) as good as all of it. The major benefit from an oil change is to refresh the additives... a few % less will mean little.
For the same reason an oil flush is probably useless and in the same category as colonic irregation.
Sounds good... but just unnecessary.
I have no idea what your reference to weak oils pumps is about.