A male inserts one end of a drinking straw into his urethra. A second male inserts the other end of the drinking straw into his urethra. The two proceed to masturbate. Upon orgasm, the semen of the first male to climax flows through the straw and into the other man's urethra. The other man mimics this act, and shoots the previous seminal load, in addition to his own, back into the first man's urethra.
My wiener is really sore from playing Ding-Dong Ping-Pong all day yesterday.