I had that happen one time. i wasn't paying attention and I flushed the toilet while I was still sitting because I was folding up some toilet paper. When I got up to wipe, I felt a tug and I'm like 'oh shit'.
Long story short, the fire department and the department of sanitation had to go into the sewer system to find my cock and trail my whole penis back through the pipes all the way to my house.
It was so embarrassing.