Mazi مذي is not Najis according to many authentic Hadeeths, e.g. Saheehat Al-Husain Ibn Abi Al-Alaa' who said: I asked Aba Abdillah ( Al-Sadiq (AS) about Mazi المذي when it touches a cloth, he said: No harm لا بأس . This and many Hadeeths in this regard are in Wasa'il al-Shia, 3:426.
Wassalam.