Not sure of that spelling, but spell check corrected it....
Anyway, I've been running for over a year, on and off and sometimes, not always, I get diarrhoea when I get back into the house. I don't feel any need when I'm running but usually about 10 mins after being home. It's always very very bloody too. Not to give too many details, but just now the toilet paper was completely red.
When this was happening last year I went to the docs, then to the hospital and they gave me a sigmoidoscopy and everything was clean as a whistle and he complimented me on such a lovely smooth bowel 
so I just don't know what this is. Do you think it could just be blood vessels bursting? Sometimes I get excruciating pain after the run as well, which is what took me to the doctors in the first place, but as far as they're concerned everything is fine.