What to do with abandoned drain/vent line?

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cmwand

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I am removing a sink from an existing basement location and don't have any immediate plans on replacing it, so I have to do something with the existing lines. What to do with the soon-to-be abandoned/unused drain is fairly straightforward because I have access to remove the drain pipe back to the main stack and cap it off.

The vent pipe, however, has me a little stumped. It continues up to the floor above and based on the floor plan of the floor above (there's a bathroom directly above the sink I'm taking out) and the configuration of the drain pipes in the attic above that floor, it's pretty clear that the vent from the basement sink I'm removing also serves as a vent for the bathroom above then continues out through the roof.

I can't get access to the vent pipe in the bathroom above to truncate the vent there (it's behind a tiled wall). It would be nice to preserve access to the vent pipe in the basement location in case I ever want to put plumbing back in, but I'm concerned about just capping off the vent pipe in the basement because I'm concerned that rain water will enter the vent line exit on the roof and have no place to drain to at the basement level. If a string of storms were to put water into the vent pipe exit on the roof, I could end up with a few feet of standing water in the capped off section of the drain pipe, which doesn't seem good to me.

Do I basically just remove the trap arm portion of the drain between the p-trap and where the vent ties into the drain line and replace the vent tee with an elbow so that the vent can drain into the drain pipe?

So, what's the best course of action here? Thanks in advance for any advice y'all can offer!

Chris
 

Cacher_Chick

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Yes, the vent must be left connected to the drain. Condensation alone will fill a vent if it is not properly pitched to drain.
 

cmwand

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Okay, thanks, I just wasn't sure if it was allowable to basically have an abandoned vent pipe connected to the drain stack without an actual trap arm as well. Logically I can't see where it would cause a problem, but I'm not a code expert so I was concerned it wouldn't be permitted by code...
 

Atomic1

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Logically, the vent would fill up with condensation and you'd have a 7' tall section of vent always filled with water. That would be a problem and is why it's not allowed by code.
 

Rufflesinc

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i ran into the same problem when renovating a kitchen. After capping off the vent pipe where the kitchen drain used to be, I went on the roof and put a 90 fernco and a 90 street elbow on the roof vent, forming an upside down U. this keeps any rain from going in
 
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