Is it necessary to handwash clothes after a wet dream due to the possibility of madhiy (pre-seminal fluid), given that maniy (seminal fluid) is pure?

If you see maniyy (seminal fluid) on your garment, it is pure but necessitates ghusl (ritual bath). If you see madhiy (pre-seminal fluid), it must be purified from the body and garment, but it does not necessitate ghusl. If you doubt whether the discharge is maniyy or madhiy, you have the option to assign it the ruling of whichever you wish. You are not obliged to wash clothes that you suspect have become impure. If you are certain they have been affected by madhiy, or if you choose to consider it madhiy, then purify the area of your garment that was affected by the madhiy. As for what you suspect might have been affected by madhiy, you are not obliged to purify it.