I just purchased a 1948 pier-and-beam in Austin. The pest control guy came to deal with rats, and asked me to locate my vent stacks. We seem to have one for the washing machine, but none is visible for either the bathroom sink or the kitchen sink.

Is this normal? Should I be looking for a vent stack terminating in the attic, perhaps under the ceiling insulation? There's definitely an unpleasant smell in the house from time to time.

Both the bathroom and the kitchen are original (though the bathroom has been updated).

It may also be worth noting that there's a guesthouse, which I believe utilizes a sump pump to deal with its sewage. The guesthouse has its own stack pipe.


Most homes will merge the vent pipes as they go up the walls so that you only have one vent exiting the roof. All vents need to slope upwards, so the guest house couldn't run the vent underground to use the vent stack in your home.

That said, if you notice that drain lines are gurgling after the water goes down (indicating suction) or are slow to drain but have no clogs (indicating it's trying to overcome the air pressure in the lines) then there may be a blockage in the vent or it may not be properly installed.

Note that for some situations, you can also have an air admittance valve to provide a one way vent (fresh air can get sucked in, but sewer gases cannot escape), which allows you to vent plumbing in a kitchen island or other location that cannot go up and out the roof.

For the odd smell, it's difficult to diagnose over the internet, but it could be a dry trap, a failed wax seal under the toilet, or a dead animal in an exhaust vent or inside a wall.

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  • Could this be the former location of a stack pipe? There's a faint line running up the wall, and it's about three feet from the kitchen sink. imgur.com/MLWqe – Juno Woods Aug 1 '12 at 18:51
  • @mohawkjohn I'd be concerned if it's leaving visible marks on the wall. – BMitch Aug 1 '12 at 19:08
  • The faint line would be from where the previous owner didn't use the right color of paint. (Did you look at the picture?) – Juno Woods Aug 1 '12 at 23:12
  • @mohawkjohn I did look, but from here it's really hard to tell. But typically, you have to look through an opening in the wall to know where the vent lines are, or look at the building plans. It's not something you should be able to see until it gets to the attic. – BMitch Aug 2 '12 at 1:02
  • It turned out that roofers apparently cut off one of the vents in the wall just beneath the attic floor. It took forever to find and we had to tear out a closet wall to fix it. The kitchen sink has no vent at all, so dirty water backs up into the dishwasher a lot. Running the disposal helps. – Juno Woods May 20 '13 at 21:48

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