Replacing the dual sink with a large sink with likely a centered drain and having to remove the existing garbage disposal as a result. The dishwasher currently drains into the disposal without an air gap (not to code). Replacing and reconnecting the sink drain seems easy enough but wondering what would be the right, to code, way to handle the dishwasher drain? do I need create some venting, or add an airgap? Our city is located in IL and uses the 2022 International Residential Building Code.

I could only find 2018 residential code: enter image description here Attached is the current set up.

enter image description here

  • 4
    At a minimum, the dishwasher drain should follow a "high loop" path, running right up to the underside of the countertop and being secured there, before continuing on down to the drain.
    – Armand
    Commented Jun 26, 2023 at 18:34
  • 1
    The air gap/backflow preventer in the first section you posted is for the water supply to the dishwasher, not the drain hose. From the section it seems that it is something that should already be built into a dishwasher at the factory.
    – Armand
    Commented Jun 26, 2023 at 18:37
  • Thanks @Armand. Both the inspector and a local plumber told us the current set up is a code violation because of no air gap for the dishwasher/garbage disposal set up. Just trying to make sure that if we update the sink we try to do it right.
    – marcus123
    Commented Jun 27, 2023 at 2:12
  • Why do you need to remove (get rid of?) the garbage disposal? I don't see a need to do so unless your new sink is simply too deep for positive drainage.
    – Huesmann
    Commented Jun 27, 2023 at 13:37
  • I am going from a 2 bowl sink with a shallow depth on one side to a large single bowl that is the standard 9-10" depth. The garbage disposal has to be removed because it wont be high enough with the new set up. We can consider redoing the whole plumbing but that is just too much money for the benefits
    – marcus123
    Commented Jun 28, 2023 at 1:04

1 Answer 1


This is actually simple.

You need a Dishwasher wye tailpiece.

Sink drain tailpiece to DW wye to 1 1/2" min P-trap.

You may have to get a DW drain extension hose to make the riser loop up to the underside of the sink.

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