All the plumbing layout diagrams I've seen show every toilet drain routed to the horizontal soil stack. Is this absolutely necessary? In the log home I'm building, the drain line at the bottom of the stack will run horizontally across the crawl space and directly under the first floor bathroom. Assuming it will be properly vented, is there any reason I couldn't wye that toilet's drain into the horizontal pipe? Or for that matter, the sink and tub drains as well?