This only happens when it rains...During the last few heavy rainstorms I noticed water running down the outside of the 4" gray PVC toilet vent pipe into the basement. Only once it dripped on the floor into a small puddle during hurricane Mathew because we had a combination of heavy wind and rain. I am unable to tell where the water is coming from, it starts somewhere up in the wall. This pipe runs straight up from the basement between walls through both first and second floors through the attic and then outside through the roof. I went into the attic and checked the pipe. I didn't see any water running down the outside of the pipe in the attic and didn't see water anywhere else around it. I had a new roof put on two years ago with new flashing around the vents. I called my roofer and he checked during a rainstorm to see if the vent flashing or roof was leaking and could not find anything leaking from the roof. It appears that somewhere within the pipe the water is coming out and running down into the basement on the outside of the pipe? Is this possible? How is this type of leak determined and fixed? Can I put a roof/cap on the pipe with holes on the sides to let the pipe vent but not let rain in, if there is such a thing or do I have to start tearing down walls?



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It could be that a nail was accidental drove into the pipe at the top or bottom plate in the wall. Over the years they will rust away and water can escape. Capping the pipe and drilling holes in the side would be a code violation because you'll be reducing the pipe size. You could put the U bend of a p-trap on it for time being. That'll keep the rain out. Depending on what you have tied into the vent I might cap off the openings and pressurize it with air to help find the leak.

I thought a nail or sheetrock screw in the pipe could possibly be the cause as well. The cap I mentioned is a purchased product from a local Home Improvement Store. It is a galvanized steel 4-way roof vent cap that fits a 4" pipe. Not sure what you mean by "what you have tied into the vent"? The pipe goes out to the septic system on one end and the other end goes out to the roof. In between there is one toilet on the first floor connected to it and on the second floor the toilet has been removed (with a rag stuffed in the pipe) due to a remodel.

i'm also guessing a nail or screw.
so, as my friend from NC suggests, get a 90 and a street 90, put them together to form a "U" and put that on top.