To the main sewage treatment plant,where it is treated to break the solids down,then eventually its pumped into a nearby river to go out to sea. If you're in an isolated area all your sewage is collected in a cesspit. The water is syphoned/drained off into a soakaway.when the cesspit is full of solids this will be pumped out and spread onto a field.
Well seal, if you ask anyone involved in sewage related works,****,crap,turd,log etc etc is known as solid once it's been flushed. The reason people do not use the common words is because as a bodily function it's still seen as a taboo subject !