As you enter the dung, make sure you have all our pots, elixirs, and panaceas off cool-down. before hitting the FINAL boss roll THREE times in forward direction, use pots, elixir, panacea, as you rolled the third time, and hit him, make sure you do not lose any of the effect of your buffs, and you will get confirm S+ drop.
Below is the link for the video proof!
https://www.youtube.com/watch?v=xvFZjo5PgG0