If you have a male turtle they will expel their sexual parts on the occasion and then they will eventually absorb them back inside. If this goes on longer then a few hours get your turtle to a vet because this will hurt the animal and can be very dangerous.
My Turtle Has Some Black Thing Coming Out Of The Butt. It Was Just Hanging Out, And It Went Back Inside. What It Is?
You should see your turtle vet as there are a lot of things that can go wrong and when they do they need treatment quickly. They are very curious and eat things that they shouldn't. On the bright side it may just turn out that it's a boy but you need to see the vet and be sure that's it at this point.