When putting oil in to your cars, do you leave the bottle end up for
a while, or as soon as it mainly empty, do you remove the one and put
another?

It always bothered me that there was still some oil in the bottle. So
I use that funnel, to collect the last drop of oil. I put the bottle
into the funnel and invert the bottle. Leave it that way for 4-5
hours and you'll get a lot more oil out. 6 quarts will often leave
enough as 1/3 quart of oil in the bottles.

I figure every drop counts.