OMFG ... really.
Dudes, think about this? Do you have hair on your head? Do you wash it with soap?
So rinse it.
Wash it when you clean your skin
then when you soap your head
Take the residual shampoo and clean your beard (if you have it with the soap "and" clean your cock and areas "again".
Then rinse it again.
So don't wash it once ... wash it twice, and if you are man enough ... try it with tea tree oil :-)