Does urinating after masterbation clear all the semen left in my urethra since my last ejaculation? i have urinated 5 times now?

Probably, but why? I occasionally find sperm in a urine sample obtained for routine health exam and ignore it in young adults. I would not think that it has any negative implications.

Agree with Dr. Ferguson. Urinating five times following ejacualation will remove the sperm from the urethra. Get HPV, Flu and Covid vaccines. Wish you good health! Safe sex: https://www.hopkinsmedicine.org/health/wellness-and-prevention/safer-sex-guidelines