My blender bottle has a rounded bottom and it's a shame it took humanity this long to solve the powder in the corner problem.
Fun look at something we probably take for granted.
Edit: this is the one I use - https://www.amazon.com/BlenderBottle-Pro45-Extra-Large-Shaker-Bottle-45-Ounce/dp/B01DPMY10O/ref=mp_s_a_1_16?ie=UTF8&qid=1531401078&sr=8-16&pi=AC_SX236_SY340_FMwebp_QL65&keywords=blender+bottle