Connecting dishwasher drain hose to unused dedicated stub-out vs to sink drain

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GoldenDaysPeter

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I’m installing a new dishwasher in my apartment, and have spent several hours researching it, but need advice. The builders 20 years ago left a 24”w space under a counter by the sink for a future dishwasher. The rear wall has a water inlet metal stub, electric outlet and 1.5” PVC drain stub. The stubs are about 8” above the floor, and stick out 2-3”. I bought in July and I’m pretty sure a dishwasher was never put there. The drain stub was covered with duct tape, which I removed to view. I don’t have a garbage disposal and never plan to have one. It seems like my two drainage options are either:

A) Connect to the sink drain. I don’t like this option due to the drawbacks of: having to drill a hole through the cabinet wall, plus it would expose my cabinet to another leak point, and I’d need to find a branch tailpiece that fits with my existing double-bowl set-up … and install it. It would also likely mean a much longer hose length, but does it matter whether a hose is 7' versus 10'?

B) Connect to the drain stub. I have concrete walls in and out. In the wall, the 1.5” pipe right angles straight down at least five inches after the bend. I poked a flexible inlet hose in, and several inches of it continued past the turn without hitting anything. My questions are:

1) I don’t know what the drain stub connects to or how far down. Does this matter, and if yes, what’s the possible issue with what it might connect to? I’ve read a lot about having a high loop - if I put a high loop behind the dishwasher, would that be enough to avoid issues? For example, does the dishwasher drain flow need a p-trap somewhere along the way?

2) The owner’s manual says: “Make sure to connect drain hose to waste tee or disposer inlet above drain trap in house plumbing and 20" (508 mm) minimum above the floor.” /// Do you think that’s only applies to if I’m connecting to my existing sink plumbing … or would it also apply to connecting to my unused drain stub? If it applies to the drain stub, is it workable to install a drain tee onto the stub?

The manual also says: “It is recommended that the drain hose either be looped up and securely fastened to the underside of the counter or be connected to an air gap. Make sure to use an air gap if the drain hose is connected to house plumbing lower than 20" (508 mm) above subfloor or floor.” // Do you think the last sentence is only referring to a situation in which I connect to the sink plumbing? Or does it also apply to the unused drain stub? The stub is only 8” above the floor, not 20”.

So far I have not been able to find an adaptor or connector to transition from a dishwasher 3/4” drain hose to the 1.5” stub out, which is about 1.8”w on the outside. Does such a thing exist and what is it usually called? I’d prefer to use the stub out drain, but I definitely don’t want to install an air gap. So if an air gap would be essential for using the unused stub out, I think I’d sooner settle for having the drawbacks of tying to the sink drain. Here is a photo of the sink area: the dishwasher will go to the right of this. I'd really love advice.

IMG_6714 kitchen sink area plumbing.jpg
 
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GoldenDaysPeter

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The photo I included in the main post was of my kitchen sink area. Here is a photo of the wall where the dishwasher will go quite close to. It shows
IMG_6681 drain pipe stub and water inlet photo.jpg
the 1.5" drain stub etc.
 

PepeLePue

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I actually came here looking for some advice for basically exact same situation, but in my search for advice found your thread. I clearly don't know what I'm doing but here's what I've gathered so far as my plan:

Add a 1.5" sch 40 trap (maybe an "LA Style" trap? for serviceability??) and then put a threaded bushing on the input to the trap, with a short nipple (galvanized or brass) and then use the dishwasher connector to attach to top of the nipple.

Should look like this as I understand:

1.5" trap

1.5" - 3/4" threaded bushing

3/4" x 4" Brass nipple


Would love if a pro could comment. I have 1x 2" and 1x 1.5". Planning on using 2" for the sink with a wye for a cleanout and then the 1.5" for the dishwasher. Any issues?
 

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Jeff H Young

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I actually came here looking for some advice for basically exact same situation, but in my search for advice found your thread. I clearly don't know what I'm doing but here's what I've gathered so far as my plan:

Add a 1.5" sch 40 trap (maybe an "LA Style" trap? for serviceability??) and then put a threaded bushing on the input to the trap, with a short nipple (galvanized or brass) and then use the dishwasher connector to attach to top of the nipple.

Should look like this as I understand:

1.5" trap

1.5" - 3/4" threaded bushing

3/4" x 4" Brass nipple


Would love if a pro could comment. I have 1x 2" and 1x 1.5". Planning on using 2" for the sink with a wye for a cleanout and then the 1.5" for the dishwasher. Any issues?
id recomend start your own thread and Ill look at it and try to reply
 

Jeff H Young

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The photo I included in the main post was of my kitchen sink area. Here is a photo of the wall where the dishwasher will go quite close to. It showsView attachment 96660 the 1.5" drain stub etc.
its unusual to have drain and water shut off behind the the D/W also unless the pipes are really low they will interfere with D/W going all the way in ? and what cut out back of cabinet to access shut off valve?
Not a lot of room to fit a wye branch in at K/S but might fit . nothing wrong atall with connecting there under sink . Remember drain hose needs to come up high against the bottom of counter top befor connecting to the stand pipe . I definately expect issues unless the cabinet is unusually deep
 
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