Q)  We recently purchased an 1862 farmhouse in lower Michigan. I had contacted you several months ago about a sewer gas smell that permeated most of our upstairs living area. It turned out that two venting stacks (one from the downstairs bathroom, one from the upstairs bathroom) were vented directly into our attic!

So, we had a handyman come out and vent them through the roof. That solved 95% of the problem, and we were odor-free throughout the cold winter months. Now, with the return of hot, humid weather, the smell has returned, although not as bad. It is clearly (in my opinion) originating from the under-the-sink area in the upstairs bathroom. I can see a horizontal, PVC drain pipe connecting to a vertical member which in turn heads downstairs to the main drain, and gives rise to the vent stack. The vent stack pipe, however, makes a quick, 90 degree horizontal turn through an interior wall into an adjoing closet, then it makes a second quick 90 degree turn to head vertically up into the attic and through the roof.

Somehow, with high humidity, ventilation seems to be inadequate, and the sewer gas is "backing up" and leaking out under my sink, into the adjacent closet, out into the upstairs hallway, etc.

So, my question is:
Is there a way to detect a leak in the pipe? It all looks to be secure, and well-glued (there is no obvious play in the pieces as I manipulate them). Is there a substance that I can paint on the outside of the PVC pipe to find the leak, or, can I paint the PVC with some sort of cement to seal any undetectable hairline cracks? Or should I just replace the pipe altogether?

Do you think the presence of the two, quick right angle turns contributes to poor ventilation, and should they be eliminated somehow? But even if you say yes, there has to be a leak somewhere for the gases to be exiting under my sink, right?

A)  If you can replace the pipes (do-it-yourself) I would do that first before you call a plumber. There's a ring inside the pipe connections and it could be missing or leaking. Start by taking the pipes you can remove and their connections apart and take them with you to your local Home Depot or Lowes. Match them up in size and replace. If this does not do the job you could have a hole in a vent pipe from a nail or a loose connection inside the wall.

Try this first and if this does not fix the problem, then call a plumber. This gas you are smelling can be very harmful to you and your family's health and needs to be fixed and the smell stopped.