Bathroom Sink Assembly Probs

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Nov 21, 2020
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I'm renting a house that's pretty old, and recently the bathroom sink became clogged after my cat knocked some things down the drain. I had to take apart the under sink pipe assembly to reach the problem. It is difficult to explain but when I took it apart, thinking this would be simple, it became apparent that the parts were too old/damaged or had been previously jury-rigged in such a way that I could not re-assemble them.

So I set about rebuilding the drain assembly. For the most part I was able to do this. The only thing I could not reassemble was a smaller pipe coming separately from the wall, which I figured was the overflow drain from the sink bowl that had previously connected to the main assembly via a PVC piece that had a secondary stem on it.

I didn't bother finding a similar PVC pipe with the extra input for the secondary drain. I figured that as long as I had built the main drain assembly and made sure not to let the sink water reach the overflow drain, i could just leave that pipe alone.

After a couple days however, i've noticed that there is a leak coming out of that pipe and dripping down into the cabinet bottom. In my extremely limited knowledge of plumbing I can't imagine what the source of this water is, other than perhaps it is backup that accumulates when other water-consuming appliances are being used. So maybe I am wrong entirely that this pipe has anything to do with the overflow drain. I'm not sure what the proper terminology for these things are but I hope this is clear enough.

My question then is this: Can i just get a rubber stopper to plug that pipe and let it be? Is there a reason that this pipe needs to be connected to the main drain assembly? Should I just give up and call a plumber?

Thanks for any insight.