Once done with the cook, I OPEN the vents 100% and allow the coals to completely ash out. The next morning, I transfer the ash, by hand (messy but insurance for sure!) into a plastic grocery bag, and then in turn to a galvanized trash can. I discovered LONG ago that throttling down and trying to snuff coals like you mention, just doesn't work. Yes I have had a flare up in a trash can because I didn't let them burn down to ash...Often I grill with sport sandals. Been doing so for decades with no issues. Chimney goes on the ground, a good way away from the grill, people, or anything flamable.
So I grill barefoot all the time...and have paid the price with the tiny speck of charcoal that drops out of the chimney. I've done some of my best swearing under those conditions.