7-Eleven BYO"C"

7-Eleven has rules to BYOC;ahem

"On Bring Your Own Cup Day, the rules are simple: cups must be clean, watertight, leak-proof and able to stand upright inside the 10-inch cutout in the in-store display, showing it fits under the Slurpee dispenser. Cups can only be filled with Slurpee drink. Let the fun begin!"

Due to the intricacies of 3d printing, I limited myself to just under a 10 inch diameter. And in theory, no 7-Eleven employee will prevent you from filling up if your container is guaranteed to fit every way, which is why I chose a sphere and not a 10 inch diameter cylinder.

This container has a 9.9 inch outer diameter and a 9.7 inch inner diameter. Due to the lid stealing some of the usable volume, it is limited to 7.581 Liters.

Considering the max diameter of 10 inches, the theoretical maximum volume is 8.58 Liters.

Making this container 88.35% efficient in this scenario.