Dishwasher air gap

Someone let me know if this installment is good. Dishwasher drain line is coming in from the bottom of the drain below the P trap. PLease describe which is the proper way. Thanks guys.

I would say not correct. No air gap visible to me, unless it is out of the frame. Hard to say why they ran it after the trap as well.

That is wrong.
Must be after the trap otherwise the gas can enter via dishwasher possibly and the hose needs to be mounted up as high as it will go for a reverse trap also to help prevent water from the sink from contaminating the DW if it backs up…

An airgap is the preferred method though not supplied often.

There is also an S-trap.

As far as location you are right Bob, my bad. Brain fart.

If it’s after the trap, isn’t that when you would get gas in there Bob?

Ian if I said it is wrong ,it means the opposite of where it is but I see your terminology correction.

I was thinking of sewer gas and going backwards.

OH the he-l with it (thanks):mrgreen:

Yep (good catch)

Gotcha Bob, just wasn’t following along for a moment there!!

Yes it’s wrong. Agree with above.

Thanks guys. So it is wrong the dishwasher should be connected above the P trap and there is an ‘S’ trap also. Right?


In your pic there is no p trap and yes it should be above the s trap.

“Should be connected to the house/building side of the trap” is how I would say it.

Anyway, the non vented “S” trap in itself is illegal.

Also if there is no visible air gap located on the sink top, then the DW drain line should be looped as best as can be. See below

Last Update: 9/14/2006
[FONT=Arial Black,Arial Black][size=4]PLUMBING AND MECHANICAL
[FONT=Arial Black,Arial Black][size=3]CODE: 2003 IPC, IRC [/size][/FONT]
**[FONT=Arial,Arial][size=3]DATE: **[/size][/FONT]
[FONT=Arial Black,Arial Black][size=3]CODE REF: IRC Section 2717, IPC 802.1.6 [/size][/FONT]
[FONT=Arial Black,Arial Black][size=3]SUBJECT: Air Gap for Dishwasher [/size][/FONT]
**[FONT=Arial,Arial][size=3]Question: **[/size][/FONT]Is an Air Gap required for domestic and dishwashing machines.
**[FONT=Arial,Arial][size=3]Answer: **[/size][/FONT]I-codes state that a dishwasher may drain through a deck mounted air-gap fitting or the drain line may be attached to the under side of the counter before connection to the disposal or drain.
From 1991 the codes have required a deck mounted air gap fitting on the drain line of a domestic dishwashing machine to protect the water supply and to prevent the contamination of the contents of a dishwashing machine. With the adoption of the 2003 I-codes the local amendment was overlooked and therefore it appears from these sections that a deck mounted air gap on the discharge drain of a dishwashing machine is not required. However, Section 2902.2.1 of the IRC and IPC 409.2 states "Air gap devices shall be incorporated in dishwashing machines …’ These sections address the protection of the potable water supply. When an approved deck mounted air gap is installed on the discharge piping system from the dishwasher it prevents waste water from back-flowing in the reservoir of the machine. Thus preventing the potential contamination of the potable water supply. The IPC Commentary states that the looping of the drain hose is to minimize the waste flow back into the dishwashing cabinet. However, by the use of a deck mounted air gap on the discharge line it will eliminate the potential for any waste water to back-flow into the machine. Thus providing positive protection for the contents of the machine and the potable water supply.
In an effort to ensure that the potable water supply remains protected in the event that a backflow occurs between the garbage disposal and/or point of connection to the drainage system. The plumbing contractor will be responsible for providing protection of the potable water supply in **[FONT=Arial,Arial][size=3]one **[/size][/FONT]of the following ways.

  1. Backflow protection installed on the potable water supply. (PBV) The PVB must be used when a deck mounted gap is not installed on the discharge piping from the dishwasher.
  2. Dishwashing machine to be installed has an approved air gap on the water distribution system of the washing machine. (Must be visually verified to be in compliance with Table 2902.2.1 IRC or Table 608.15.1 IPC)
  3. Installation of a deck mounted air gap fitting or a device similar on the discharge line from the dishwasher to the point of connection to the drainage system will provide equivalent protection the potable water supply and contents of the dishwasher.
    Note: With the adoption of the 2006 I-codes the deck mounted air gap on the domestic dishwashing drain line will be added to the amendments.