Dishwasher drain air-gap -- cheater vent?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by gardner, Apr 2, 2007.

  1. gardner

    gardner DIY Senior Member

    My dishwasher will drain into a trap that is quite a ways from my sink, that serves only the dishwasher. I have 1-1/2 ABS with a dishwasher nipple on the side. Above the nipple I need an air inlet to provide an "air gap". I am trying to decide what to do.

    Maybe I can build a snorkel out of 1/2 copper to exent above the ABS.

    Or I could install a cheater vent at the top.

    What would be best setup to ensure the air-gap, but limit he possibility a rush of dishwasher outflow could back-up?

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

    gardner DIY Senior Member

    I went with the cheater vent. I have an 8-inch run of 1-1/2 ABS above the dishwasher nipple and a cheater vent screwed in at the top with just enough room to get it in and out under the countertop. Seems to work and no noise from the water being pumped in.

    Attached Files:

  3. curious about how to eliminate the noise too

    Thank you for posting this.

    So far, I know that diswashers and washing machines need air space to drain, and that this is why they cannot be "hard-wired" into plumbing.

    I don't know whether that vent can provide sufficient air for all possible needs, and I can't see (too dark in the photo) whether your DW drain is tied tight with a band coupling....

    I am very eager to know how to eliminate the noise
    so if anyone else can help explain whether this installation is totally good or not, I for one will appreciate knowing.

  4. Gary Swart

    Gary Swart In the Trades

    Yakima WA
    In my totally unprofessional opinion, you're OK if you will loop the drain hose and fasten it on the underside of the counter. It seems to me that you have essentially the same configuration as if you were going into a sink drain in a "normal" installation. The Studor will give you plenty of venting.
  5. gardner

    gardner DIY Senior Member

    Yes. The end of the DW drain is 3/4 rubber that is a tight fit + a hose clamp. This is a pretty solid seal.

    Unfortunately not enough hose for this. The drain hose does run in a loop up to the top of the DW and back down though, before leaving the side of the DW.

    This is not a proper AAV, but a cheap spring-loaded cheater-vent. It definitely opened easily though -- I could suck air through it with no apparent force. I feel confident it would break any siphon action sucking the water out of my DW.
  6. jimbo

    jimbo Plumber

    San Diego
    What you have is NOT an air gap. An air gap means there is literally a space...between the end of the hose and the drain pipe. A washing machine standpipe qualifies, and your standpipe might pass muster if you got rid of the AAV and left the standpipe open. Of course, if this is a concealed location, you could have unseen overflow.

    An AAV should never be used on a pumped drain, because it relieves negative pressure, but cannot relieve positive pressure.

    In my opinion, your inspector will disapprove this installation for the above reasons.
  7. kordts

    kordts In the Trades

    exurban Chicago
    Where is the p-trap? That cheater isn't venting anything. It needs to be on the other side of the trap.
  8. create standpipe equiv

    true it isn't venting 'anything' meaning that it isn't acting like a plumbing vent does, on the sewer side of a P trap.

    I think it is designed to create a standpipe, assuming it lets air both IN and OUT.

    Which it doesn't, if it is an AAV.

    I am considering building an 8' high standpipe just to minimize the noise. I would Wye into it and keep the air space opening very small.

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