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.
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.