The musical episode of NBC's Scrubs doesn't hit the air until Jan. 18, but visitors to YouTube can now check out a pair of numbers starting Friday. In addition to the Zach Braff- Donald Faison duet "Guy Love," which has been making the rounds for weeks, the site will also make available "Everything Comes Down to Poo," sung by Braff, Faison and guest star Stephanie D'Abruzzo ( Avenue Q).