Reason for 2 sink drain pipes? Advice needed

[fbcbeer]

Here is a picture to the laundry room plumbing before drywall and after the cabinet was installed. There are 2 drain pipes going into the same main drain. Temporary PVC caps have been installed on the pipes since this picture was taken.

Why is there a 2nd sink drain pipe, and how would I connect the sink to the drains pipes?

Thank you, in advance!

 

[Sparky617]

No idea why. I'd just use the one that lines up closest to the sink and cap the other. Even two bowl kitchen sinks only use one drain line.

 

[fbcbeer]

Bumped.

Any other thoughts from anyone? Is it possible it could be for an air release valve or something?

 

[Sparky617]

There is a vent next to the washer drain line. I'd just cap the extra, looking at the picture without drywall you can see there is only a connection between the two stub-outs. Everything goes to the same drain line.

 

[Eddie_T]

It's possible that one had an air intake on it to keep a trap from siphoning dry but you could always uncap it and add an intake should the problem occur.

 

[Flyover]

How old is the house? Where is the laundry room situated within it? This is probably way out there, but I wonder if the room used to serve a different purpose, for which two drain pipes were needed?

 

[Eddie_T]

THere are times that wish I had multiple drains. The cross pipes under my triple basin sink limit under sink storage more than straight runs to a drain would.

 

[Sparky617]

THere are times that wish I had multiple drains. The cross pipes under my triple basin sink limit under sink storage more than straight runs to a drain would.

Especially with a large disposal hanging below one of the bowls. Doesn't seem to be the case in the OP though.

 

[Whatmeworry]

Can we ask where this set of mistakes is located? Certainly looks like new construction but totally misses code for any place I've been! Metal studs are not what I'm used to but that setup for the laundry drain looks like a mistake!
Is it a drain or a twisted bowel?

Then the way the weight on the pullout faucet is arranged seems like a real problem if it is connected as shown. I would not want the line wrapped around the supply lines??

But for the question, I would have to guess there is some serious difference in the codes they were following. Not what I would expect as the only option seems to be a poor one using a vaccuum breaker of whatever name.
The problem without a system to break the vaccuum as water goes down the drain at left, is that the water left in the drain trap will tend to be sucked out and down the drain as the water goes out!
I feel a far better solution would have been to tie a vent into other existing vent as I've drawn here. This is very simple and works a longtime without fouling to give trouble. Often much cheaper for parts as well!

But at this point, it may be best to go with what they've built and use an "admitance valve" of this sort. They tend to be expensive and also a bit of added maintenance if/when they get a bit of age and stick open or closed. Notice that they have failed will be when sewer gases are coming into the room! Not something I like to build in for myself!
https://www.homedepot.com/b/Plumbing-Valves-Air-Admittance-Valves/N-5yc1vZca2v