I had a plumber do some rough in work for a bathroom remodel and was planning to install the sink/vanity myself. It’s a single sink. Why would there be two pipes leading to the same drain pipe and how would one even hook this up? None of the other sinks in the house have this and I can’t seem to find anything like it online for a single sink setup.

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  • 3
    May be incorrect, but my guess would be that one may be for ventilation. I'd give the plumber a call to check it out – cutrightjm May 4 '18 at 17:06
  • It’s hard to tell the sizes from the picture. May be a clean out which would eventually be caped with a threaded plug. – user76730 May 5 '18 at 2:28
  • "For ventilation"? What does that mean, @cutrightjm? – isherwood Jul 17 '18 at 16:49
  • Voting to close. We can't really know the plumber's intent with this non-standard installation, and OP hasn't been back. – isherwood Nov 21 '18 at 15:03

The only reasonable explanation I can think of is that he didn't know the height of the vanity he was plumbing for.

If you try to hook up a sink on a tall vanity (~34" high) and the drain is roughed in for a standard vanity, you'll need an extension for your p-trap, and waste space.

In this situation, I would decide which fits your sink the best and cut-off and cap the other one.

Give him a call and find out for sure.

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Check whether one has a tee fitting (as opposed to the sweep that the other one probably has). If that's the case it may be intended as a cleanout access.

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