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, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
Maniyy is known to be a thick white fluid that is emitted with forceful gushing and a sensation of pleasure, and it smells like date-palm pollen. Mathi, on the other hand, is a thin white fluid whose emission is often unfelt. Please, refer to fatwa 82518.
If you detect the smell of Maniyy in this discharge, then it is Maniyy and necessitates Ghusl; and if you detect the characteristics of Mathi, then it is Mathi and necessitates Istinjaa' (cleaning oneself with water after answering the call of nature) and ablution. If you doubt which one it is, then the view that we adopt at Islamweb is the view of the Shaafi'i School; that you are given the choice to decide which discharge it is and act upon the relevant ruling.
Lastly, we would like to alert you (if you engage in masturbation) that masturbation is prohibited and that the one who engages in it is obliged to repent of that. For more benefit, please refer to fatwa 81150.
Allah knows best.