You Only Gotta Wash Under Your Armpits - Just the Armpits

Gintama.: Slip Arc · Episode 14 · “You Only Gotta Wash Under Your Armpits - Just the Armpits”

Consists of episodes animated from unused manga chapters, before returning to the Silver Soul Arc on January 8, 2018. Porori is an Onomatopoeia for something (mainly water) falling.