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We recently got new counters installed with a deep sink. The garbage disposal outlet is now just about level, if not a little lower than the drain. I understand that the sink will likely not drain in this configuration. We do have a dishwasher drain standpipe which connects to the same drain pipe albeit at a lower point:

enter image description here

Is it possible to have a shared trap between the disposal and the dishwasher standpipe?

I’ve been reading different forums and have come up with a few ideas but don’t know which one is the best/most up to code (we live in Colorado).

  1. Move the standpipe to the above drain and connect the disposal to the lower one.
  2. Connect the disposal output to the current standpipe with a T and use the single trap for the sink/disposal and dishwasher. Cap the other drain opening.
  3. Connect the dishwasher drain to the disposal using a high loop and connect disposal outlet to lower drain (Not entirely sure if this would meet the CO code, don’t want to put in an air gap as we just had granite countertops installed). Cap the other drain opening.
  4. Connect a wye to lower drain opening and have a separate trap for the disposal and the dishwasher standpipe.

I appreciate any and all help. If there is a better way to do this I am all ears. Thanks!

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    Option 1 sounds good.
    – Ecnerwal
    Aug 26, 2022 at 21:18
  • 1
    Not sure why you even have a separate dishwasher standpipe. Normally the dishwasher drains (after a high loop or air gap) into the disposal - the connection is near the top of the disposal in your picture. Aug 26, 2022 at 22:04
  • I agree that in most installations that I've seen, the dishwasher is connected to the disposal unit. However, there is a benefit to having them kept separate: If the disposal unit is full (someone didn't or forgot to run it) it can limit the drainage capacity and cause the dishwasher to overflow out of the sink. Depending on the sink size and the dishwasher flow rate, you can end up with water on the floor.
    – pdd
    Aug 26, 2022 at 22:14

1 Answer 1

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I cannot speak to your local code requirements, but where I live it is standard to connect the dishwasher to the disposal unit and only use one p-trap.

However, there is a benefit to having them kept separate: If the disposal unit is full or plugged and someone runs the dishwasher, there is a chance that the disposal unit's drain will be restricted enough that it cannot accommodate the flow rate of the dishwasher discharge. This will cause water to fill the sink and if the sink cannot contain the capacity, water will overflow onto the floor.

Therefore, in my opinion, option 1 is your best bet.

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