Dishwasher drain diameter

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Julie Sandell

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Hi all,

My new, high efficiency dishwasher won't drain, and the repairman (not very confidently) said it was the fault of an overly narrow drain line under my sink. Could that be true? Currently, the dishwasher drain hose connects to a 1/2" copper pipe that runs from the bottom of the cabinet under the sink, up a high loop (with 90 degree turns), then into my sink drain (after the p-trap, which I know could be a problem, but doesn't worth re-plumbing for unless it gets smelly).

My old (noisy and inefficient) dishwasher never had this problem. The repairman said the diameter is too narrow for the new, low power pumps to push through. True?

Thanks for your advice!
 

Terry

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What brand of dishwasher do you have?
As far as I know, 1/2" has been fine for dishwashers as long as it's on the pipe coming from the dishwasher.
We use 7/8" after the air gaps, but but if you're using a high loop, the 1/2" should have been fine.
Options for connections in the Seattle area are

johnson_tee_b.jpg


Johnson tee, with a 1/2" copper line feeding it.

sink_dw.jpg


Air gap on countertop, draining either to the disposer or a tee before the p-trap, or second p-trap from wall.
A high loop in some cases. We install Bosch with a high loop and not the air gap.
 

Julie Sandell

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It's a Bosch SilencePlus50. I attached the drain hose that came with the Bosch (larger diameter) to the small copper piping. All of the copper plumbing was already in the house. Could the 90 degree bends (at top of the high "loop") in the copper be the issue?
 
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