Thumb sized piece of white and pink tissue came out during peeing. not pregnant and have a copper iud. what could this be???

Pink tissue: JessicaD7 ~ you dont say but is this associated with a recent period. What you have seen is either a thin sliver of vaginal tissue (some anti-fungal creams can slough the vagina), or its a piece of endometrial tissue as the lining of the uterus can be shed during or soon after a vigorous menstruating. In either case there is nothing to be worried about. Its part of the normal process.thank