I gotta be honest, I hated that scene. I guess I'm not a fan of to people suffering, even when shit is involved. I dunno, I just felt really bad for the poor girl the whole scene. And it was especially weird with how comedic it was all supposed to be. I wasn't sure what to feel, but aroused definitely wasn't it.
Also, it didn't help that it used every stock diarrhea sound effect under the sun. Seriously, those sounds were ripped straight from Dumb and Dumber.