Hello. welcome to healthcaremagic. In males, the urethral opening serves as the outlet for both urine and sperms. Under normal circumstances, due to the pressure created during micturition, the sperms are not allowed entry into the urethra during urination. Similarly, during sexual excitement, the urethra serves as the passage for sperms and not the urine. There are no valves and at times, some amount of intermingling may be possible. Due to the push and pull during sexual intercourse or masturbation
, the urinary bladder
may feel the extra pressure and hence the feeling of urination. This is absolutely normal and there is no harm if you pass urine following masturbation. Wish you good health.