I don’t see how masturbating with soap has any increased risk of soap in the urethra than normal washing. Especially when you wash yourself everyday. It would also matter on how often you do it. If you’re jerking it with soap every time you jerk it yeah you increase the likelihood but if it’s a once in a while thing it would be a negligible increase in odds.
I can’t believe I just put that much thought into jerking it with soap.