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Discussion Starter · #1 ·
Recently replaced sink and garbage disposal only draining when turned on. The disposal is brand new so no food / clogs whatsoever, the P-trap drain assembly is new / clean. Running water will start to pool in the sink and only drains when the unit is turned on.

The disposal drain is a few inches higher than the main drain as it should be, so hopefully no issues there. This is also in an island with a vent loop as pictured. Any advice / ideas would be greatly appreciated as I anticipate this will be a major issue once the dishwasher is installed.


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A "Handy Husband"
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Disconnect the drain from the disposer, with a pan under the disposer, run water and see if it drains without the disposer running.
The results will show whether it is a disposer or a piping issue.

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Discussion Starter · #6 ·
Is your loop vent connected to a wall vent - as shown in the above diagram (bottom right corner) ?
That is my assumption, the connection is made below concrete slab (this is a condo building). There was a disposal here before that did not have this issue. The only other change is that this is a deeper sink, however the disposal drain is still higher than the main drain so shouldn't be any gravitational issues.
 

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Discussion Starter · #7 ·
Disconnect the drain from the disposer, with a pan under the disposer, run water and see if it drains without the disposer running.
The results will show whether it is a disposer or a piping issue.

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Tried this, draining the short elbow from disposal into a bucket. No pooling in the sink at all after a few minutes, so that rules out anything wrong with the disposal.
 

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I think the Chicago loop calls for the horizontal pipes below to be upsized in order for that drain to function. I would try two things:

(1) reduce your faucet flow to slow and see if the sink still backs up with low flow, the idea being there may be a venting issue prohibiting draining only during full flow.

(2) if you did it exactly as pictured in the diagram you attached, then there should be a cleanout on the dry side to clear the pipe in case a blockage occurs and debris gets trapped on the dry side as water rises and will not go back down when the blockage clears. Open that CO plug and see if everything suddenly works once that's open. If so you have a vent issue.
 
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