Why do I have a vent pipe capped off in the basement?

First I would like to say Thanks to Terry for putting this site and forum together. It has proved helpful to me more than once.

I'm just a woodby homeowner trying to keep water going in the right direction.

After lots of confusion over what the occasional leak near the end of a questionable vent pipe I finally ripped up our downstairs bathroom wall and found it. The previous owners drilled through a vent pipe for a bathroom fixture and it leaked from the inside out, down the outside of the pipe and around the subfloor. It is in an outside wall and damp to wet at the subfloor and even on the sill on the foundation. It had been there for a while though so the leak was smaller for the most part. Ok, that being said in the summer it is completely dry. Hmmm, in the fall and winter it was getting wet again. Besides the original questioning of what the cause was (siding, window right above it, etc) I also was confused as to why a builder would route a vent pipe into the basement and terminate it with a cap. Maybe for the washer or a future basement bath? We have that on the 1st floor and no fixures in the basement at all.

This pipe from what I can tell is terminated in the basement to just a cap and goes all the way up into the attic and then over (without any other apparent connections) over to the main vent stack. It may have connections that I can't see for the washer in the downstairs bathroom but it would have to travel through the walls and or ceiling. It is 3" pvc. There is a bath upstairs but not directly over this one.

After temporarily fixing that hole as water was slowly creaping out of it my thought was that it was just condensation inside of the pipe dripping down. I still questioned where the water would go at the end of this pipe. Today, I opened it up to permanently repair the hole and water is gushing out of it. The hole is 4 ft up from the cap. We had about 14" of snow the other day and I'm now thinking that the water is not all condensation rather it is also any thing coming down the main vent?

So here is my real questions...
What is this pipe really for?
If I fix the hole and leave it (filling up with water and not draining to anything) will it be ok or am I asking for problems down the road?
If this pipe is supposed to be there for future use and not fill with water is there another issue that I've yet to discover?

Sorry for the long explaination I'm a bit confused on why this pipe is where it is and my wife is not too happy with any more walls being interupted if at all possible.

BTW: before we bought the house and noticed this, they had a plumber come over and said it was not a plumbing issue and that it was a siding issue. The siding people were happy to reside that small corner of the house with new wood and siding and said everything was dry when they opened the wall. Huh, 6 mo later still leaks. I just went to my papers from the sale of the house and noticed that that plumber charged them for looking into that issue not to mention they resided for no reason. He def. makes my do not call list.

Brian

Many homes are piped for future rough-in, the vent pipe may be capped off for a future bathroom.

I would not be surprised if you had plumbing in the floor for a toilet and perhaps a tub or shower, all just waiting to be tied into that capped off vent.

Vents that go through the roof, do collect water, that normally drains all the way down.

I would repair the leak that the previous owners made, and call it good.
Mark the location, and at some point if you decide to go for another bathroom, you will know how to vent it.

water in the pipe?

Thanks. So you don't think that the water in the pipe will be an issue? I just drained it and noticed that there was about 4' of water built up inside. Is this OK?

I could drain it once and a while I guess from the bottom cap. And if it did not leak during the summer my guess is that most of it evaporates to some degree.

What do you think?

Brian

I don't think that it will be a problem. I wouldn't bother draining it, either. Now that the hole is patched, if it ever filled up high enough, it would drain into the sewer system from the tie-in way up high. If you were worried about it, you could tie it into the sewer system down in the basement as it would be if it was in actual use say for a bathroom, but that may be more trouble than itis worth. My unprofessional opinion.