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Old 11-17-2011, 10:41 PM   #1
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Dishwasher Drain Install w/o Sink

I am building a new house and wondering if it would be possible to attach the dishwasher drain directly to a separate 1.5" P-trap behind the dishwasher. In other words, is it possible to hook up the drain of a dishwasher without attaching the drain to the tailpiece of a kitchen sink?

I would like to do this for several reasons:

1) Since the discharge would not be going into the p-trap of the kitchen sink, I believe the discharge would be completely silent.

2) I believe the sink would drain faster if it was draining at the same time the dishwasher was discharging.

3) I would not be cluttering up underneath the kitchen sink with electrical and plumbing for the dishwasher - I would run the electrical directly behind the dishwasher and also plumb the water supply directly to the dishwasher. Therefore, nothing under the kitchen sink would relate to the dishwasher.

Any thoughts (good or bad) would be appreciated. If you don't see a problem, please advise on what type of connections I could use to convert from 1 1/2" PVC to the discharge hose of the dishwasher.


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Old 11-17-2011, 11:58 PM   #2
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Dishwasher Drain Install w/o Sink

How are you planning to connect the water and drain of the dishwasher if you put the plumbing behind it? What if your dishwasher is leaking and you want to shut it off? Pretty sure that the valve for the appliance has to be accessible.

99% of the time people aren't using their sink at the same time the dishwasher is running. If you think about it, you usually only run the dishwasher after the dishes are done, don't you?

As far as noise, i'd venture to guess that the noise that the motor in the dishwasher makes is louder than the water discharging into the sink drain for the 5 minutes that it's actually on the pumping out cycle.

I'd say conventional hookup is best. It really isn't that much more stuff under the sink anyway.

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Old 11-18-2011, 09:04 PM   #3
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Dishwasher Drain Install w/o Sink

Thanks for your response.

As far as being able to turn off the water, the dishwasher will be plumbed through a manifold with shutoffs. So I could shut it off at the manifold.

As far as the drain itself, I would simply attach the drain to the underside of the cabinet and push it back into the cabinet just like pushing a refrigerator back that is attached to a water line. Or just like you have to do when the drain is attached under the sink.

The washing action and motor of our last dishwasher was almost completely silent - I suppose due to the insulation and quality of the dishwasher. However, when it drained into the disposal you would hear it draining - the rush of the water. I am hoping to eliminate that noise this time.
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Old 11-21-2011, 01:10 PM   #4
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Dishwasher Drain Install w/o Sink

I still haven't found a fitting I could use to attach a dishwasher drain straight into a p-trap. The only fittings I've ever seen/found are on the tailpiece of a sink drain or a disposal. Any suggestions?

However, now I'm wondering if I actually found a fitting if I would be double trapping the kitchen sink? The kitchen sink is 7' from the 2" drain coming up out of the slab. (All under slab plumbing was done by a licensed plumber - the kitchen sink has not/was not moved from the original blue prints - crazy to me why he didn't come up a "little" close to the sink?) This 2" drain travels about 15' before it ties into the main 4" drain - nothing else is on this 2" drain. To plumb the sink I am going to run a 1 1/2" drain horizontal (1/4" drop per foot) from the kitchen sink stub out to the slab stub out. This horizontal run will have to go through 4 2x6 studs. Between the kitchen sink stub out and the concrete drain stub out, I would like to put in a 1 1/2" tee pointed straight up to which I would attach a p-trap at a height higher than the kitchen sink p-trap - maybe another 3 inches. A vent will come off of the horizontal run about 2 1/2 to 3' from the kitchen sink stub out. The vent will be between the dishwasher p-trap and the concrete stub out. This is the complete right to left layout: 2" concrete stub out, 2" to 1 1/2" reducer, 90 degree sweeping elbow, 4' horizontal 1 1/2" pipe, 1 1/2" sanitary tee turned straight up which will be vented out the roof, 1' horizontal 1 1/2" pipe, 1 1/2" sanitary tee turned straight up to which a 3" to 6" long vertical pipe would be attached and then a 90 for the dishwasher stub out, 2' horizontal 1 1/2" pipe and then a 90 at the end of this pipe for the kitchen sink stub out. Would this be considered double trapping?
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