Garbage disposal causes debris to come up in other side of sink

Old 07-05-01, 01:50 PM
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My kitchen sink is a standard aluminum 33" double sink, with a garbage disposal on the right side. All PVC pipe, the home is less than 20 years old. I rarely use the disposal, and never for anything large enough to be picked up and thrown into the trash can; no eggshells, etc. On a pretty regular basis, when I turn on the disposal, the left sink gets backwash of all the crud left in the pipes. The only way to clear it out is to fill the right sink fully with clean water, and use the disposal while draining, repeating a few times, until no crud backs up in the left sink. At the end of this cycle, both sides will drain easily and quickly when filled with water. This has been going on since I've lived here, 15 years. I asked a plumber once about it while he was here on another problem, he looked at the plumbing and remarked that the plumbing configuration was "strange". Where the drainpipe exits the house, just to the left end of the sink, it's a straight pipe with a "U" and a trap plug going up the the left sink; a 45 degree cutout from the main pipe goes over the the right sink with another "U" and a trap plug. Would you possible be able to provide a detailed description, or maybe a picture, of how the pipes should be configured? Or is there something missing in the configuration (one-way valve?) which should prevent the backwash?
Old 07-05-01, 03:53 PM
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I have had two houses that were plumb correctly and would both do what you describe if I waited to long to run it. In these cases running it evey day took care of it.

Good Luck
Old 07-05-01, 10:31 PM
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if this is a recent occurance you have developed a diminished capacity in the sink line. where the two lines
from the sink join is where you may find the stoppage or it can be further down stream requiring a roof shot. another factor that will cause this would be the drains under the sink are installed improperly.when build up occurs in the sink line the water will take the path of least resistance
when forced down the line by the disposal,if it cant go down the intended drain line it will come up the other side instead.
Old 07-07-01, 04:41 PM
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If the tee where the disposal and the other side of the sink connects, does not have a baffle in it, then this will be the cause, when water rushes towards the tee when disposal gets turned on, the water will move in both directions, to fix this install a baffled tee in that spot.

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