When either severe seasonal allergies, or a virulent sinus infection causes you to digest copious amounts of mucus through post nasal drip, the impending explosive intestinal distress will result in a bowel movement consisting of mucousy tendrils of hot fecal napalm which will feel as though the Old God is using your sphincter as a portal into this world.
Fred: Wow, the old Gods sure took out their fury on the toilet
During the act of unprotected coitus, immediately post ejaculation the male holds his partner is a pseudo-snuggle until the sensation of impending urination strikes. While the penis remains inside the vagina/anus the male relieves himself, allowing his urine stream to flow freely, flushing out any seminal deposit and filling the body cavity with urine.
Note: When the flush'n'fill leads to a aggressive yeast infection, it is called the sourdough croissant.
Don't worry about getting knocked up, I gave you a flush'n'fill, though you might smell like a pickle jar now. Warn me if you develop a sourdough croissant.