Peace be upon you. According to Grand Ayatollah Khamenei and Grand Ayatollah Sistani, the practice of istibra with nine squeezes ensures that any moisture that comes out afterward is considered pure if there is a possibility that it is urine. There is no need to perform ablution (wudu) for it. However, if someone has ejaculated, they should perform istibra with urine before doing the nine squeezes. This is not a condition for the validity of the ghusl (ritual bath), but if they neglect it and then experience moisture that resembles semen, it will be treated as such, and they must perform ghusl for it, regardless of whether they performed istibra due to difficulty urinating or not, unless they are certain that no semen remains in the passage. Therefore, if you performed istibra with urine, then did the nine squeezes, and afterward experienced a fluid and are unsure whether it is pure or not, that fluid is considered pure. May you be successful in all good.