Fleshy substance? Trying to understand what you are talking about. I think you are referring to sediment. That usually consists of one or more of microscopic particles, various kinds of cells, debris from your urinary tract, or mucus. If it is a little bit, that can be normal. But do you have any pain? This also happens if someone has a urinary tract infection. Diabetes can have this occur along with it too. An infection, kidney stones, medication you take can all cause it. Probably ost common cause though is dehydration. Drinking enough? If it continues and especially if you get any other symptoms with it, call your doctor. https://www.healthline.com/health/sediment-in-urine#When-to-see-a-doctor