Single sink drains slow - please help!


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Old 11-28-18, 02:36 AM
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Single sink drains slow - please help!

Good morning, all.

I just finished installing a new sink and piping, but for some reason the sink refuses to drain normal, As it's new piping, I don't think it's clogged and I was hoping to get some advice.

Please see the attached image. In the image the sink drain goes into a P-trap, then merges with the dishwasher drain pipe before exiting to the waste water pipe. The white adaptor on the top of the stack is an Oatey sure vent admittance valve.

When I did the first install, I didn't have the vent installed, so the sink didn't drain quickly. After doing some research, I read I needed to install a vent, so I did that. But it still does not seem to have made any difference.


As I said, if I put water in the sink it will take forever to drain as if there's a severe clog in it somewhere. Prior to this install, we had a double sink setup, and we never had this problem.

Any advice would be appreciated. Thank you!

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Last edited by PJmax; 11-28-18 at 10:46 AM. Reason: added pic from link
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Old 11-28-18, 02:53 AM
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Everything from the AAV down should really be 2" pipe. The AAV should be extended upward so that it is as high as possible under the sink... right next to the countertop, if possible. And the fitting where the trap makes its turn down should be a wye or sanitary tee... the tee you used does not look like a sanitary tee. Is it possible that it's upside down? Any elbow below the cabinet should be a DWV 90... or long sweep 90.

You never had a problem before because it was likely sucking air from the unused sink drain.
 
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Old 11-28-18, 04:09 AM
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Will a 2" pipe make that much of a difference? The entire system is made of 1.5" piping, so it would be rather costly for me to run it all the way back to the sewage pipe.

I don't think the wye is installed upside down. Please see the attached photo. I would have thought the vent would allow enough air through to permit the sink to drain properly.

At this point I'm just thinking of simply returning the sink and going with a dual setup again.

Thanks,

https://imgur.com/a/N1aeZeW
 
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Old 11-28-18, 05:19 AM
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One easy test is to remove the AAV and see if the sink drains any better. If it drains well without the AAV you may have a bad AAV. They are a mechanical device and can fail or be made incorrectly (that's why you can't bury them in a wall because you may need to change or service it).
 
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Old 11-28-18, 08:05 AM
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Thanks for the reply. I tried that before and water ended up shooting up through the port and soaking the cabinet.

I do do have another one coming in so I will try that one.
 
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Old 11-28-18, 08:10 AM
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That is why I said the AAV needs to be installed as high as possible, hopefully beside or behind the sink where the top of it will be close to or above the water level of the sink. It can't suck air if a slow drain is causing it to back up.

Extend it higher.
 
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Old 11-28-18, 08:13 AM
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Even with the short elevation of the AAV you should not have water shooting up out of it (still it needs to be mounted higher like SXleeper mentioned). I would snake the drain line to make sure something isn't clogging it.
 
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Old 11-28-18, 10:50 AM
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Is that short white/clear flex line the dishwasher connection ?
That's not correct either. If that is the dishwasher..... the sink will over flow into it if the drain is slow.
A dishwasher line needs to go all the way up to the bottom of the countertop and then down to the drain.
 
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Old 11-29-18, 06:37 PM
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Appreciate everyone’s responses.

So just to be clear and I don’t have to waste more $$$ on piping:

- place the AAV as close to the bottom of the counter as possible
- put the dishwasher waste pipe above waste wye for the p-trap

Anything else I should do?
 
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Old 11-29-18, 07:04 PM
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Doesn't the DW drain pipe also need to connect upstream of the trap to prevent sewer gases from emitting from the DW?
 
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Old 11-29-18, 07:11 PM
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That is why the dishwasher loop is supposed to go way up to the countertop in a high loop. It makes its own trap in the dishwasher line that way.
 
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Old 11-29-18, 07:36 PM
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But don't you need water in the line to block the gases?
 
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Old 11-29-18, 07:42 PM
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Common sense would dictate that there will always be water on the dishwasher side (low side) of the loop.
 

Last edited by XSleeper; 11-30-18 at 07:33 AM.
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Old 11-30-18, 04:44 AM
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It is most common for the dishwasher to feed into the sink drain right below the sink and before the sink trap. They even make a fitting just for the job. But the backing up and coming out of the AAV when it was removed is still not a good sign. Have you snaked the drain line to make sure it's clear?

 
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Old 11-30-18, 05:36 AM
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Thank you, everyone.

So here's a rough drawing of what I've gathered from the group. Does this look correct?

https://imgur.com/a/pQWGy03
 
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Old 11-30-18, 05:50 AM
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The dishwasher outlet will always come out of the dishwasher near the floor of the cabinet as Dane pictured. Other than that it looks fine.
 
  #17  
Old 11-30-18, 06:00 AM
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I think the plumbing code was not made very clear here and should be clarified. There are two independent requirements.

Doesn't the DW drain pipe also need to connect upstream of the trap…
You are correct and it is relevant to this thread, (1) a high loop is required (or an air gap) and (2) the drain connection must be before the p-trap (either to a wye on the sink tailpiece or on the disposer). Both (1) and (2) are required.
 
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Old 11-30-18, 06:06 AM
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Thanks, to everyone who responded. Working on a new design.
 
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Old 11-30-18, 06:14 AM
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Ok, I think I see what you mean. The flexible pipe for the dishwasher needs to move up higher, but the actual waste pipe can stay where it is then (near the cabinet base)?

Like this?

https://imgur.com/a/RVCIs80
 
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Old 11-30-18, 06:21 AM
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(2) the drain connection must be before the p-trap (either to a wye on the sink tailpiece or on the disposer). Both (1) and (2) are required.
Thanks for confirming. That's what I thought. Glad we're able to have a conversation amongst each other with the goal of helping the OP solve his issues. Have a great day everyone.
 
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Old 11-30-18, 06:23 AM
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I think your diagram is correct. It meets both requirements: the DW drain hose is looped high, and the DW drain hose is connected to the sink tailpiece, in other words it's connected in above the trap as is required.

I was just making the point that both things are required because it sounded a little fuzzy to me.
 
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Old 11-30-18, 06:32 AM
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Just for reference to confirm a dishwasher should be served by a trap. 2015 Residential Code P2717.2: "The combined discharge from a dishwasher and one or two compartment sink shall be served by a trap..."
 
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Old 11-30-18, 06:58 AM
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The picture in post #15 is correct. The picture in post #19 is not correct. The DW drain hose has to connect to the plumbing above the p-trap as you have it in the picture in post #15.
 
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Old 11-30-18, 08:14 AM
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Great. I appreciate this collaborative approach to solving this issue. Now I'll put it into effect and see how it works out.

Again, thank you everyone!
 
 

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