Can a dishwasher discharge into a standpipe?

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Lllammma

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Hello all,
I am installing a dishwasher, but the deep sink means that the discharge hose would be just at the minimum level recommended by the manufacturer and I'd rather not be right at the limit.

Is it permitted to have a separate dedicated standpipe with its own trap for the discharge (similar to a washing machine)?

To complicate matters, it is in an island. My plan would be to connect the trap arms of both p traps to the same vertical drain and share the island loop vent.

Thanks!
 

Lllammma

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I may have answered my own question through a thought experiment. If the top of an open standpipe is below the flood level of the sink, water could theoretically come out the standpipe if you filled the sink to the top and pulled the plug... Especially if the dishwasher discharges at the same time. Although in practise this seems unlikely, I suspect it is not permitted? If that is the case, my next question: is there a permitted way of creating a dedicated standpipe that's connected to the sink drain after it turns horizontal below the floor?
 

jadnashua

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If you're willing to put an air gap in the counter, that would work. In places, they are required, and prudent anywhere. Lots of places sell them, and I'm not saying this is the best place or the best item, but it gives you an idea of what they are and what they look like. You can find them costing less than $10, to over $100.

https://www.plumbingsupply.com/airgap.html
 

Widgit Maker

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You are making things unnecessarily difficult. You may use an air gap as stated above, or you may use a "high loop". With the high loop method, the discharge hose is simply secured to the underside of the counter top. Either method prevents contaminated water from the sink entering the dishwasher. As far as the dishwasher is concerned, with either method the the discharge level is the counter top.
dishwasher high loop.jpg
 

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Lllammma

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Thanks - the issue with the high loop is that the manufacturer specifies a minimum height above the floor of 18" for the final connection to the barb (after looping). In this install, that inlet is just barely above 18 and just "feels" too close for comfort for me. But I guess as long as it's not <18 it's fine. I just generally prefer a better margin than fractions of inches :)

Around here, air gaps basically don't exist - I have never ever seen one installed... avoiding additional counter penetrations is of course preferred from the end user perspective.

I suppose I will take an accurate measurement and decide based on the true height of the discharge inlet once it's installed.
 

jadnashua

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An air gap does exactly what it says...provides an air gap between the outlet of the DW to the drainage system. While a high loop is commonly used, and works nearly all of the time, it will NOT prevent contamination or siphoning all of the time, which is why an air gap is better. Depending on the sink and counter installed, sometimes you can use one of the holes in the sink for the installation of the air gap without putting a new one into the counter.
 

hj

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I have no idea why they specify the 18" minimum, because it is illogical since there is nothing about the drain connection that has any bearing on a "minimum 18" connection.
 
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