The process involves blood being sucked out of the body.
The former NRL premiership-winner, who converted to Islam in 2008, revealed his use of hijama cupping therapy, an age-old Muslim procedure in which small glass cups vacuum blood from small incisions.
In the picture, Williams is hunched over a chair with six blood-spattered bell-shaped cups attached to his back. Two longer shaped cups protrude from his neck.
"Detox time", the Rugby World Cup winner titled the post, followed by an emoticon of two hands raised in celebration and another representing clear skin.