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Draining kitchen sink flushes toilet

Posted by jandree22 (My Page) on
Mon, Aug 2, 10 at 20:21

Since we moved into our house, a rapidly draining kitchen sink flushed our toilet. Sometimes the tub would do the same behavior, but not with the same consistency. I suspected a clog in the sewer vent, but after attempts to unclog, no luck... vent is wide open and still happens.

I think I figured out what's going on but not quite sure what to do about it. I've attached an image of my plumbing lines into the main sewer line in the basement. I'm speculating that the rapidly draining kitchen sink is coming down the black line so rapidly, it's shooting straight across horizontally to the white line and interfering with the flow of vent air down the main sewer line. As a result, the falling water is vaccuuming the toilet.


The solution that comes to mind is relocate the entrance of the black kitchen sink/tub line lower, or have it enter the sewage line at a 45* vs laterally. As shown below, I have an untapped entrance to the line further down adjacent to the slop sink.


Any thoughts would be great, thanks!

Follow-Up Postings:

RE: Draining kitchen sink flushes toilet

Sounds like someone left out some vents or the sink vent and tub vent are clogged.

The kitchen sink needs a separate vent from the one in the basement.

RE: Draining kitchen sink flushes toilet

Ah I see. Thanks for that info. I don't know for certain that it's not connected to the main vent up to the roof... just didn't think to check. Will take a closer look tonight.

RE: Draining kitchen sink flushes toilet

"Maybe the plumbing wasn't done professionally."

With joints that appear to be between ABS (black) and PVC (white) it is very doubtful it was done by a plumber, and probably never inspected.

There is no approved cement for joining ABS and PVC.

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