All praise be to Allah Alone, and peace and blessings be upon His Messenger, and his family and Companions.
The basic state of the body and clothes is Taharah (purity), whereas contingent doubt counts for nothing. If you wash the place you think is soiled with Madhy, you can offer Salah and there is no sin upon you. As for
Madhy itself, it is Najis (impure). If you discharge Madhy, you should wash your whole penis and testicles, and sprinkle water over the part of your body and clothes that were soiled with Madhy, as the Prophet (peace be upon him) ordered
‘Aly to wash his penis and testicles, perform Wudu’ after discharging Madhy, and sprinkle water over the soiled parts of his clothes. (Part No. 5; Page No. 383) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.