Fart Horn
The sound emits when the ass has created a complete seal with the toilet seat and a fart is produced, vibrating through the toilet and makes a distinguished low-pitched sound, audible through walls and floors.
Planted comfortably in a stall in a restroom, Jim heard what could be non-other than a fart horn sounding from the stall two stalls down from him.
butt horn fart
a fart that emulates that sound a horn
Dirty Johnny ripped a butt horn fart in class today.