Two drain pipes connected together BEFORE p-trap. DIY’er wanting to understand why, and learn best next steps.

[Jconly]

So, I’ve been living here for over 10 years..
I’m about to plumb in an espresso machine and it’s drain - and in the process have finally gotten more curious about my plumbing.

Specifically, why do I seemingly have two drain pipes connected in a horseshoe shape, before the sink drain?

When I first moved in there was no garbage disposal. Then within the past year I installed the disposal. I left the dishwasher drain as is. Everything has been going great, as far as I was aware.

But in the process of making space for a water filter under the sink, I decided to rotate the p-trap back parallel-ish with the wall to free space. In the process of toying with the plumbing a few things have popped up, and have made me curious.

Firstly, I’ve realized that theres water sitting higher above the p-trap, into the dishwasher drain hose. I guess this is to be expected?

Then after re-plumbing the disposal (I might make some changes still - advice appreciated!) I’m noticing water is sitting up to that level of its output - which I guess makes sense given the previous realization and the new horizontal run. Also noticing with a trial run of the washer that I’m getting a TOUCH of water pushing into the disposal itself.

So I got curious… shouldn’t it be going down? Gravity and all.
I began to think more about the weird drain I have after the trap, and looking closer.
And While I was draining water from the sink, I loosened the hose clamps on the large drain pipe to adjust the p-trap location a bit. Water started to come out the top joint.

After tightening up, and upon further inspection with some hot water from the dishwasher drain… I’m realizing that the pipe is hot going up and to the right of the trap and back down. It’s immediately cool below the trap, which I was not expecting!

I’m guessing that Instead of flowing down after the trap, it seems to be going to the RIGHT, up and around.

So, what’s up with these two pipes anyway?
Would love to know why they both exist - and what’s going on.
Do I have a clog?

I’m in a NYC duplex. Kitchen is ground floor, another level below, where the utilities enter the building itself.

Thanks in advance for your input and advice!

And feel free to tell me I’m doing things wrong - I’m not a plumber, obviously.
Was planning to put the drain from the machine directly to the disposal, and putting a 3/8 compression T off the cold water line into the filter.

 

[wwhitney]

Is this kitchen sink in an island? And is the DWV fitting obscured behind the garbage disposal in the first picture a simple quarter bend? (I assume so but want to verify).

If so, what you have is a bad implementation of an island loop vent. The "horseshoe" is supposed to be up as high as possible (almost touching the countertop), and instead of a horizontal pipe at the top, there should be two diagonal segments (45 degrees off plumb) joined by a quarter bend.

Your description is certainly consistent with a clog in the drain on the left, below the san-tee. You can remove the trap and snake that drain to hopefully clear it.

If this kitchen sink is not in an island, then you have an inappropriate implementation of an island vent. Although NYC probably has its own plumbing code or heavy amendments to a standard code, so it's possible that they have expanded the allowances for island vents.

Cheers, Wayne

 

[Sponsor]

 

[GReynolds929]

Looks like a poor attempt at a island loop vent. What you're describing indicates there is a clog downstream of the drain and the water is taking the next available route which is through the vent loop. I would snake the drain and go from there.

 

[Jconly]

Thanks so much for the helpful responses!
It is indeed an island. I'll do a little more research on the loop vents.
Looks like that was the keyword I was looking for.

What might not be obvious from the photos, there IS a slight angle on the horizontal pipe.
15degrees maybe... the left side is higher. These pipes are just connected with some rubber and metal collars, so I'll try to re-arrange to get a little more elevation and slope.

A poor implementation indeed - this place was mostly likely put up pretty quickly on a budget. Typical NYC construction. A lot of sloppy ends.

And thank you for confirming the other plumbing checks out, that I'm most likely dealing with a clog. I was worried about my disposal plumbing being the culprit. Will need to run out and grab a snake.

Much appreciated!

 

[CanadaGuy]

I believe your dishwasher drain should be connected to the inlet at the top of your disposal. This allows the junk from the dishwasher to be ground up whenever you rush the disposal.

 

[Jconly]

I believe your dishwasher drain should be connected to the inlet at the top of your disposal. This allows the junk from the dishwasher to be ground up whenever you rush the disposal.

That does seem like a benefit.
I might swap that, and put the espresso drain down below.
Have a clear line just above the trap would also be beneficial.

I disassembled the loop vent tonight.
There was a thick clog just after the trap in the iron pipe, fully sealing the drain.
I ran about 25 ft of snake down into the drain, and felt as if I just kept having to push through stuff till I could push no further.

Begs the question of my plumbing is not cut out for the disposal…
Although it’s only been in for a year max, and I’d say it’s a safe bet this is the first time that drain has ever seen a snake since construction, in the early 2000s.

Again, I greatly appreciate the feedback. Thanks for the advice.