A fart that travels through a turd before exiting the ass, creating a very pungent aroma. A milk fart will occur in the few hours leading up to a bowel movement, as the turds have made their way close to the butthole, creating the filter that your gas will pass through on it's way out.
"Damn.. that bitch Brenda just laid out a milk fart, I'm fucking nautious."
When you have a sticky fart while you have swamp ass, and then the swamp ass mixes with the sticky fart into a sludgy paste.
I had a sticky fart earlier, but I thought I was fine. Little did I know that I also had swamp ass, and they mixed. Now I have to throw away my underwear because of a simple milky fart.