I recently replaced the plumbing from the bathroom sink all the way to where the drain pipe comes through the wall. In the process I cleaned out what I can only assume was about 50 years worth of sludge from the pipe. I also noticed that I can't find any venting for the sink plumbing. I am also thinking that given the placement of the tub drain and the lack of vents coming out of the roof that the tub may not be vented either. The house is about 100 years old. Would it be typical for the plumbing in an older house to not be vented? I may just be missing the vent but when I feel inside the wall there is only a pipe leading down to the main sewer but no pipe leading up to the roof.