Washing machine backing up into bath tub.

Hi all,
I recently moved into a 1927 Tudor style home with a finished basement. The basement has a second kitchen, laundry in a utility closet and a full bath. When the washing machine is draining durning the spin cycle I'll hear a gluging sound coming from the (basement) kitchen sink. Occasionally water from the washer will back up into the bath tub. Even more puzzling...when the water backs up into the tub, the water in the toilet gets sucked out. The tub back up/toilet suckage don't happen every time I use the washer but the sink noise does. The washer drain pipe is a standard looking 2" plastic standpipe with a Studor air admittance valve for venting. Trying to figure out if I have a drain issue, a venting problem or a combo of both. Ideas?

As I understand it (I'm not a pro), an AAV can only be used if there is a true vent in that system somewhere, not as the ONLY vent. Sounds to me that you either have a clog somewhere, or they did not vent the system properly in the first place.

I'm assuming (big assumpsion!) that the basement was vented correctly when the plumbing was installed and the AAV was just to vent the washer into the existing system. After doing another load of laundry this morning I think I've figured out the "glugging" sound coming from the sink is the water in the trap being pulled out, as I can smell a pretty strong odor of sewer gas coming from the sink. Question is, would a clog cause this? If so, would it most likely be in the washer drain line to the sewer main or the main itself? If not, could it be a venting issue? Help!

The glugging sound of the water being sucked out of the sink trap is a clear indication of a venting problem. When the water flows down the sewer drain it creates a vacumn that usually pulls air in from a vent line. In your case the vent is either non existent or has become blocked (unlikely).

Try removing the mechanical vent temporarily to see if that eliminates the glugging. If so then it is probably malfunctioning and should be replaced. While a mecanical vent is never ideal - it can work in a situation where running a proper vent was not done - but mechanical vents do wear out - as may be the case for you.