Let me just preface this post by saying it is entirely in no way at all comparable to my post about Grandma's Marathon this summer. Any attempts at a comparison will leave you sorely disappointed. For this I apologize. But NOTHING NOTHING NOTHING could compare to how painful that was.
I'm pretty sure that running and sh*ting have gone together since the beginning of time. Pheidippides may very well have sh*t himself and then died of embarrassment--I'm fairly certain we'll never know for sure. They may have just pretended it was from exhaustion to let Pheidippedes die with a bit of dignity. There comes a time in every runner's career when he or she will deal with a similar situation. I think that if you don't almost sh*t your pants at least once (not go all the way, however) while you are training for a marathon, then you just aren't ready.
But anyways, from the beginning....
"Blue" bibb marathon camp
There are many interesting things to entertain one before the start of a large marathon. For example: Japanese tourists doing Thai-Chi synchronized to music for a warm-up, 'Team for Kids' members doing jumping jacks, French-men in disposable haz-mat suits frolicking about, seeing how many times one can ration a 3ft. long piece of BYO toilet paper (ahem, about 6).
Starting line, Verazzano Bridge, Staten Island, NY
Certainly the largest contingent in Europeans wearing head-to-toe Spandex I've ever come across. It's kind of unfortunate for all of us that it's tight right there, sir....
Miles .001-2: There's something slightly creepy about middle age men peeing off a bridge just because they can...as thousands of innocents stream by and attempt to avert their eyes
Miles 2-13.1: Brooklyn, NY "Welcome to Brooooouk-lynnn"
Mile 2: 'You're almost done' I hate you.
Mile 3: Onset of the Stomach of Death. This is no ordinary 'I have to go' urge--this is the nausea-rising, chilling in the toilet-room all afternoon feeling. At first you try to deny it; if I just forget about it, maybe it will just smash into itself and wait patiently for another 3.5 hours for me to finish. Please, SOD, go awaaaaaaaaay!
In a race of this length it becomes a balancing act, you see, sugar is an SOD's worst enemy, but your muscles best friend. For some reason denial doesn't work during a marathon...there are so many people around, but yet, you are so so alone in this thing.
Mile 11: I can hang on...maybe...just wait it out until 12
Mile 12: There comes a point when a runner just can't ignore the Stomach of Death any more. There was really no choice at this point--either go in the big blue box or go in my little blue Nike shorts. The line looked manageable at least, and I was second-up. Maybe had that 200-year-old non-English-speaking Japanese man not cut in front of the entire line, this next near-horror could have been averted. When you dive into your little blue plastic box for a bit of privacy you expect it to be on solid ground, or more accurately, flat ground. Well, this runner found herself in a tippy porto. You're in a porto at your most vulnerable and it is rocking back and forth, seemingly going to fall off the curb--is this a joke, I mean, really?!?? The balancing act that ensued would make any surfer proud. At one point, I feared I might go over.
My thoughts at that moment could be summed up into this: 'If this thing tips over how am I going to explain why I didn't finish? How does one tell everyone they were covered by gallons of human excrement?? They will have to take me away and vaccinate me for every disease known to man. Nightmare.' Nightmare narrowly averted. SOD taken care of several minutes later, balancing act successful, excrement bath narrowly averted. Whew. What did I eat? Or more importantly--what ate ME??
Mile 15.9, Middle of Queensboro Bridge, Queens/Manhattan, NY: Oh, there up-ahead, is the 16 mile marker, that means water...I guess I will eat a packet of super-charged snot-textured sugar-maltodextrin goo...oh, water station fake-out grrrrrrrreat! It is possible to gag so hard it feels like someone is stabbing you in the ribs, just in case you were wondering.
Mile 17: Return of SOD Part Deux. Ick.
Mile 25: I begin to hear the crowd erupting in laughter as I approach, before I can check my shorts for stains, I see him--or I should say--his ass cheeks--he is a mulletted man wearing a bright-green Borat thong. Yes, letting (most of) it all hang out. Priceless.

Mile 25.5: Legs start to get tired...damn you, SOD...I could have gone so much faster.
Mile 26.2: DONE!! But now we are being herded like a bunch of stunned cattle and the SOD refuses to wait. The volunteers laugh at me when I ask how far the bathrooms are from here. A quarter mile later, I beg the medical staff to let me use their blue toilet boxes, after contemplating fence-hoping and then walking salmon-style up-stream, I reach it. Each individual's heaven could be a function of the situation they are in at a precise moment...and mine was there waiting, a stable, non-tippy, TP-laden blue box of happiness.
Well, that's about it. See, I told you it wasn't as good (bad) as last time. 
All done, wrapped up in fleece coats!