I hate to continue this subject, but I tend to agree with Arkkeeper. Given that Ageans, Indus, Sumerrians, Minoans,etc had many homes with some type of indoor facilities 3000+ years ago, it is not inconceivable that in many locales that some way would be fashioned. I would say that other than solid rock (in which case there many still be a way) or marshland, the soil could be dug down enough for many if not all homes to have a sewer system installed and properly maintained.
Not even counting the overtly magical solutions of magic items or magical sewer keepers, there are also ecological solutions possible for some of the larger towns, namely creatures such as gelatinous cubes or the like which may be in a chamber built underneath the main city.
Joe