I have never done a full marathon. I have done several 10 mile races and a half marathon. I think the bathroom is the most under-discussed component of any long distance run. It's pretty important to get in a good poop prior to the run starting. If you have a 8am race time and you normally crap at 9am every day. I think it would be smart to begin waking up at 6am and trying to retrain your body to go to the bathroom at 7am. No joke.
Nothing is worse than having to crap mid run :)
I'm in the worst running shape ever. I applaud all of you.
Go get it, SeanBot!