Jimmy Wah's appreciation for the way a solder's ankle "so elegantly curve into his boot" in Good Morning Vietnam echoes my affinity for a well-fitted trash bag into a step trash can. Over the years, I've settled on the following technique to get great trash bag fitment on nearly all step trash cans.
There is no set nomenclature across step trash can manufacturers, so for the sake of our short-term lexicon, "bin" refers to the black inner portion of the trash can held by Brook from Zappos.
This technique uses the "bin hole" (yeah, I just made that up) located on nearly every bin I've ever encountered like in the picture below:
Drape the edges of the trash bag over the opening edge of the bin, and locate the bin hole:
Using a digit, push the trash bag from the outside of the bin, through the bin hole like so:
Locate the trash bag portion protruding through the bin hole:
Grasp the protruding trash bag portion, and firmly pull towards the center of the bin:
When pulled taught, the edges of the trash bag will now tightly conform to the bin profile and the assembly should fit snugly into the trash can body like so:
I've been doing this for so long that I'm wearing a Gen 1 Pebble watch in the pictures I took way back in 2015 on an Apple iPhone 6 to show a friend; and since then, I've not needed to refine this technique any further. The trash bag gets so tight to the bin profile that I hear Goldmember appreciatively describing it as "toight like a toiger".