Gas Moisture
Residue of fart - A slipperiness between the butt cheeks caused by poo particles and moisture released from a fart.. Fermenting Gas moisture is thought to be the cause of Butt Cheese or Honey Butt.
I've been fartin so much I have gas moisture - I need to pop to the toilet to  check, I'm sure the residue of all my farts will be brown. 
or
This Mexican food has given me gas moisture (morning after, wipe check)