I just wanted to see what you guys think on this. I've been doing a pile of remodeling and repairs on an old river cottage. The toilet is slow to drain. The tub taps in past the toilet and the tub is not vented... everything else is vented properly (tub trap gurgles when toilet is flushed). The question is... what is to keep that tub from backing up with sewerage if the sewer line to the septic tank stops up? How would you plumb a drain to prevent this without using a back flow preventer? Is this addressed in a code somewhere?