Purity: Urination After Ejaculation
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 347:
It is recommended that one urinate after ejaculation; if he does not urinate, and after performing ghusl some fluid comes out about which he does not know whether it is semen or some other fluid, it is ruled to be semen.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)