system
A chat on subreddit /r/NoStupidQuestions
human
If you want anybody near your under-carriage, wash all of it well; fresh is best and widens your options.
gpt
Some people really need this spelled out for them:

You need to wash your dick including under the foreskin if you have it. You need to wash your balls, perineum and crack. You need to use soap and rub firmly. Letting soapy water run down your body isn't sufficient.