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 Why would kitchen sink vent pipe get clogged?
Author: Anonymous User

The context: Double sink, with a garbage disposal, PVC 1.5 inch piping under the sink.

All started a while ago.

First, dishwasher or sink would occasionally not drain but I could force it through by running garbage disposal with lots of hot water and other sink plugged, which effectively used it as a pump forcing lots of hot water into the drain.

Second, septic smell started appearing right after dishwasher cycle started. Never after or before that. I started wondering if we are having a went problem as the plumbing book was saying that vents prevent traps from loosing water and letting septic gasses going up the pipe. Still not fatal.

Today, lost drain big time. Garbage disposal leaked, water everywhere, lousy picture. Blamed old disposal, thought it lost the seal. Went to the local store and got a straight PVC extension with a slip joint to replace a t-junction that connected disposal into the drain. I thought to reconnect one sink straight into the drain, and leave the other sink waiting for the new disposal to come in.

Now it gets interesting, connected everything together, opened water and nothing goes out of the drain. Took everything apart (full of water), got a manual 20 feet snake and fed it all the way into the drain. It came clean and fine. Since the kitchen is connected to the same drain the nearby bathroom is using, and there are no problems in the bathroom, I thought that chances of a far away blockage were small. So, I remembered about the septic fumes and thought that no venting could also prevent water from reaching the drain, and I fed the snake up into the vent, went halfway with some getting stuck here and there and pulled it out to inspect. To my big surprise, the snake came all covered in sludge big time.

At this time I will reattempt to feed the snake in there again.

Big question, what's going on? Why is the vent pipe is sludgy? Was I forcing the water into the vent and it deposited disposed garbage into it? And, really, what should I do now?

Update: after some fishing with the snake in the vent, I've tried to run water again and it drains now. Don't know about the smell as it requires the disposal to be working, and I am waiting for a replacement unit now. Still, why sludge in the vent? Do I have a bigger problem I am missing?

Edited 1 times.

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 Re: Why would kitchen sink vent pipe get clogged?
Author: hj (AZ)

The disposer acted as a pump. so it would push 'debris' up the pipe, but it would normally only accumulate in a horizontal line, which you might have if the vent has to offset past a window. A plugged vent ONLY prevents drainage if there is also a plugged line downstream, which is probably your real problem.

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 Re: Why would kitchen sink vent pipe get clogged?
Author: Anonymous User

Right, there is a horizontal piece to avoid a window right above the sink.

So, the plan is to wait until the drain clogs again (hopefully eventually but not soon) and use a longer snake that time. Meanwhile, stop using disposal to flush through minor clogs as it pushes debris in the wrong place (the vent).

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