Is it obligatory to remove ointments from the anus after urination if they have been contaminated with urine, or is it sufficient to wash them with water while leaving them in place due to the difficulty of their removal?

If there is doubt about whether the discharge has contaminated the ointment, then the ointment is pure and there is no need to remove it, because the default assumption is purity. However, if it is confirmed that the discharge has mixed with the ointment, then the ointment becomes impure and cannot be purified. It must be removed, and its removal is possible by wiping it away and washing its place until it is highly probable that the area is pure.