Single Bowl Sink but Two Disposal Lines

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JerCap
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Single Bowl Sink but Two Disposal Lines

Post by JerCap » Sun Oct 08, 2017 6:41 pm

Hi all. I’m getting ready to replace my two bowl kitchen sink with a single bowl sink but I have two drain lines going in to the wall. Right now each of the two sink drains have a designated disposal line. When I switch to the single bowl sink what do I do with the other disposal line? I’ll have a dishwasher and garbage disposal on the new single bowl/drain sink. Can I just cap one of them off? Is having one of the drain lines designated for the dishwasher drain a bad idea? Thanks.
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A. Spruce
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Re: Single Bowl Sink but Two Disposal Lines

Post by A. Spruce » Sun Oct 08, 2017 8:05 pm

Yes, you can cap the drain you are not using.

The DW really needs to be hooked up to an air gap, this prevents ingestion back into the DW of sewage if/when the drain backs up. You can either use an above sink air gap if you've got a hole for it, or you can leave it under the sink as high as possible. From the air gap you can connect the DW to the nipple on the disposal, there is a knock-out plug inside the nipple that will need to be removed first.
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Shannon
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Re: Single Bowl Sink but Two Disposal Lines

Post by Shannon » Sun Oct 08, 2017 11:21 pm

Yes I have no idea why they would have two drains anyways as it was not needed for the double bowl sink either.
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JerCap
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Re: Single Bowl Sink but Two Disposal Lines

Post by JerCap » Mon Oct 09, 2017 6:01 pm

Thank you, both for the responses. My area dorsn’t require an air gap but I agree the DW drain hose needs to be elevated above the nipple. If I cap one of the disposal lines should I leave the p trap or cap it close to the wall?

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A. Spruce
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Re: Single Bowl Sink but Two Disposal Lines

Post by A. Spruce » Mon Oct 09, 2017 6:36 pm

You need a trap between the open sink and the sewer line, you do not need a trap on the one you will be capping.

If you are not going to install an air gap, at least put a loop in the discharge line that goes above the nipple.
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Shannon
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Re: Single Bowl Sink but Two Disposal Lines

Post by Shannon » Mon Oct 09, 2017 6:53 pm

Cut the p trap off and cap horizontal pipe.
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