Ernesto Priego has a post called Night Soil over at Never Neutral. But judging from the tone of the piece - a note (a) as to how he's got an eye infection & (b) how he's enjoying reading Sean Finney's The Obedient Door - I don't think that what he means by the term is what I mean when I use it.
In my very early childhood, younger than six, the town where I lived had neither sewerage nor septic tanks. Instead there was an outside toilet - a dunny - that had, behind & beneath the wooden bench on which you sat to crap, a small outside door through which the nightly (?) collection of excreta would be made. Hence the term night soil.
Probably every family has a much-loved story somewhere in their history about sitting on the dunny seat & having the night soil collector take the pan away from underneath them. A couple of local additions to the myth include the time the night soil truck overturned in the main street of an even smaller town a few miles away. &, what is not myth but reported fact, the time a local night soil carter got charged with breaches of the health regulations because he also delivered the milk at the same time.