All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ʻalayhi wa sallam, is His slave and Messenger.
You should know that what the woman is required to wash in Istinjaa’ is the visible part of her private parts only. She is not required to wash the inside of her private parts. The visible part is the one that is visible when she sits down to relieve herself. If she washed this part, then she has performed the purification properly and the impurity has been removed. If she experienced any wetness afterwards, it is declared ritually pure because no consideration is given to what is inside her privates parts, which she is not obliged to wash.
The scholars held that the impurities that have not been separated from their place of discharge are not subject to a ruling (neither declared impure nor pure). Shaykh Ibn ‘Uthaymeen said:
“The impurity that has not been detached from its place of discharge is not subject to a ruling. It is not declared impure except when it is detached from it. What is inside the human body is declared neither pure nor impure. This is accurate, and this is why some scholars held that if the ‘Alaqah (clinging clot) in the uterus is transformed into a Mudhghah (lump of flesh) and then a pure embryo, it is not accurate to say that it has become ritually pure through transformation. The Muslim jurists excluded the ‘Alaqah that develops into a Mudhghah and then a pure embryo from the impurities that become pure through transformation. However, some scholars refuted this exception, arguing that the clot inside the womb is declared neither pure nor impure according to the principle that an impurity that has not been separated from its place of origin is not declared pure or impure.”
Thus, you come to realize that the impurity that has not separated from its place of discharge does not render impure whatever comes in contact with it. Mathi is not declared impure, for instance, unless it comes out to the visible part of the private parts. If this part is washed, it remains pure, and any pure discharges that come out afterward are declared pure. This is clear and should not cause any confusion; praise be to Allah.
Allah knows best.