Dishwasher Air Gap hookup size mismatch?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by stinkyDavis, Nov 27, 2006.

  1. stinkyDavis

    stinkyDavis New Member


    I have a dishwasher but no garbage disposal. I want to install an air gap. It's my understanding that the standard sizes are:
    • dishwasher discharge hose: 5/8" ID
    • dishwasher wye sink tailpiece: 5/8" OD (takes 5/8" hose)
    • air gap inlet: 5/8" OD (takes 5/8" hose)
    • air gap discharge: ?
    I just bought new dishwasher discharge hose, 5/8", and a dishwasher tailpiece, copper, 5/8" fitting. They had a number of these in plastic as well, all 5/8", and one straggler with a 7/8" fitting. I'm looking for an air gap with a 5/8" discharge fitting so that I can make the hookup directly from airgap to tailpiece with a single length of hose, using no adapters.

    The only air gaps I can find have a 7/8" discharge fitting, which it seems is used with a garbage disposal. Some websites refer to this as "standard", so I'm thinking there must be a non-standard air gap for connection to a dishwasher tailpiece (5/8") when you don't have a disposal. But I can't find this kind of air gap.

    Does anyone know of an air gap that meets this requirement? Is the only way to do this with a reducer? Am I nuts?

    Last edited by a moderator: Sep 28, 2007
  2. hj

    hj Moderator & Master Plumber Staff Member

    Cave Creek, Arizona

    7/8" is standard and it is the size of a brass branch tailpiece connection. There are 7/8" plastic ones or you just clamp the 7/8" hose down to the size of your connection.
  3. Buy the standard Air Gap with the 7/8" discharge and switch the tailpiece connection to 7/8".

    The reason why I would go with the norm is because if you stick with 5/8" in the full swoop, the dishwasher depending on how fast it discharges will cause resistance and that Air Gap will always be leaking.

    7/8" is the best way to go without any worries. Do not reduce to 5/8" using 7/8" heading towards it; it will back right up to the Air Gap.
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