My German Shepherd will get poop as you describe if I overdo it with the organ component of her meal, especially beef heart or liver. It took quite a few nights of black, liquid, stinky poop on the floor in the middle of the night to realize it was too rich for her to eat in large quantities. Since I dialed down the organ component a bit, she's been fine. That said, it can't hurt to have a checkup just in case.
Solomon - black DSH - king of kitchen raids (11)
Gracie - Mutterooski X - scary smart (9)
Jaida - GSD - tripod trainwreck and gentle soul (4)
Heidi - mugsly Boston Terrier X - she is in BIG trouble!!! (3)
Audrey - torbie - sweet as pie (11 months)
Patrick - blue - a little turd (but we like him anyways) (6 months)
Boo, our Matriarch (August 1 1992 - March 29 2011)