He's a link to a condensed history of outhouses and privys. Rather interesing reading I suppose.

http://www.bottlebooks.com/privyto.htm

But I tend to agree with ravells, especially for the fantasy genre of games. It is fantasy, not necessarily medieval. My campaign is set in a world of high magic, and has one rich merchant's house that has the garderobes going to a non-dimentional space (sort of like a bag of holding does) and a permanant control temperatue so that the only fireplaces are those used for relaxation. However, the poorer inhabitants of the land use the traditional chamber pot and street.

If I were running a historical game, I'm sure I'd research things a bit more.