I don't claim to be a biblical expert because I'm not.   I'm only saying that this is interesting....   and kinda weird.  But the next passage quoted below makes no ifs, ands and butts about it, it talks about eating poop.  If you ask me, which you didn't, that's weird!

BTW, in Ayurvedic medicine from India, cow dung and urine is used for medicine.  So, if a man were "clean", why not his own?

 http://bible.cc/isaiah/36-12.htm.  Each of the (XXX) is short of the translations, e.g., KJV = King James Version.

Isaiah 36:12
But Rabshakeh said, "Has my master sent me only to your master and to you, to speak these words, and not to the men who sit on the wall, who will eat their own dung and drink their own urine with you?"  (WEB)

But Rabshakeh said, Hath my master sent me to thy master, and to thee, to speak these words? hath he not'sent me to the men that sit upon the wall, to eat their own dung, and to drink their own water with you?  (ASV)

But the Rab-shakeh said, Is it to your master or to you that my master has sent me to say these words? has he not sent me to the men seated on the wall? for they are the people who will be short of food with you when the town is shut in.  (BBE)

And Rab-shakeh said, Is it to thy master and to thee that my master sent me to speak these words? Is it not to the men that sit on the wall, that they may eat their own dung, and drink their own urine with you?  (DBY)

But Rabshakeh said, Hath my master sent me to thy master and to thee to speak these words? hath he not sent me to the men that sit upon the wall, that they may eat their own dung, and drink their own piss with you?  (KJV)

But Rabshakeh said, Hath my master sent me to thy master and to thee to speak these words? hath he not sent me to the men that sit upon the wall, that they may devour their vilest excretions with you?  (WBS)

But Rab-shakeh said: 'Hath my master sent me to thy master, and to thee, to speak these words? hath he not sent me to the men that sit upon the wall, to eat their own dung, and to drink their own water with you?'  (JPS)

And Rabshakeh saith, 'Unto thy lord, and unto thee, hath my lord sent me to speak these words? is it not for the men -- those sitting on the wall to eat their own dung and to drink their own water with you?'   (YLT)