What does the black debris look like?
And what kind of pressure do you feel that makes you believe those are roundworms? I've been feeling this kind of pressure occassionally for about 8 months that feels like my colon is about to explode, kind of like the feeling you get before a burst of diarrhea but the pressure is higher up the colon and no diarrhea is coming. It got me fooled a few times - I would run to the bathroom but nothing, and it subsided after a while. Maybe that's the roundworms moving around inside of me.