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Sink drains when garbage disposal is on only

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  • Aug 27th, 2021 7:00 pm
[OP]
Deal Addict
Jun 11, 2010
1500 posts
913 upvotes
ottawa

Sink drains when garbage disposal is on only

Hey RFD,
I have a stupid plumbing issue I need more support to solve. I have a sink, that goes into a garbage disposal, that goes into a p-trap, that then drains to the main stack. The sink only drains when the garbage disposal is on, otherwise it backs up, also if I drain with the disposal on, then turn it off before it's fully drained, water will return almost as if it's being blown back up my sewage line, sometimes with a bit of force.

I've taken out the garbage disposal and completely inspected it, no clogs, turns freely.

I've examined all aspects of the p-trap, no clogs.

I've re-installed the garbage disposal, left the clean-out under the p-trap open, and ran the water with a bucket underneath, drains perfectly fine into the bucket.

At this point I've eliminated the garbage disposal, and p-trap as part of the issue, so I let it clog up and used a plunger to try and clear the blockage, no luck. Then I fed a 15' snake into the line and hit no blockage.

I'm about to call a plumber obviously, but I thought I'd ask here in case anyone has some other ideas - I'm still baffled at how the line can drain when the garbage disposal is on if there is a blockage? Without it on it doesn't drain a centimeter so if it is blocked turning on the garbage disposal should not help at all. My next thought was the stack that goes to the roof for airflow but I have no idea how to diagnose it from that end.
12 replies
Deal Addict
May 16, 2017
2346 posts
3067 upvotes
Disposal can act as a sort of pump, so can overcome some drain flow issues. I had similar issues with frequent clogs downstream at a cleanout just down from where the sink line joined the stack.

Elevation and slope of the line compared to the outlet of the disposal all the way to the stack?

Or, there is a partial clog downstream and you are getting some backup into the stack, which then flows back.
[OP]
Deal Addict
Jun 11, 2010
1500 posts
913 upvotes
ottawa
robsaw wrote: Disposal can act as a sort of pump, so can overcome some drain flow issues. I had similar issues with frequent clogs downstream at a cleanout just down from where the sink line joined the stack.

Elevation and slope of the line compared to the outlet of the disposal all the way to the stack?

Or, there is a partial clog downstream and you are getting some backup into the stack, which then flows back.
Thanks Rob - been trying the plunger for about 30 minutes this morning to no avail. Might try snaking it again before giving up and calling someone in. I tried vinegar/baking soda as well, plus dawn and boiling water, no luck so far.
Deal Expert
User avatar
Nov 28, 2016
22791 posts
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Out west
Do you use the disposal much? If not, get rid of the thing. We have had one in each of the last 2 houses. Loud, smelly and issues like you have.

I never understood the concept of them. All that food waste just causes extra stress on city septic treatment.

And they are a 100% no no on a septic tank

The clog down the line is probably from the build up of vegtable peels, etc down the line.

Probably a reason why so many cities dont allow these anymore
[OP]
Deal Addict
Jun 11, 2010
1500 posts
913 upvotes
ottawa
WikkiWikki wrote: Do you use the disposal much? If not, get rid of the thing. We have had one in each of the last 2 houses. Loud, smelly and issues like you have.

I never understood the concept of them. All that food waste just causes extra stress on city septic treatment.

And they are a 100% no no on a septic tank

The clog down the line is probably from the build up of vegtable peels, etc down the line.

Probably a reason why so many cities dont allow these anymore
We hardly use it at all, it's only for items that accidentally make it down the drain into the garbage disposal. The odd thing is the dishwasher drains fine and connects into the sink drain that I can see in the basement. So it would have to be somewhere between the p-trap under the kitchen sink and where it connects to the dishwasher line. I might try snaking it again but snaking drain lines is such a pain.
Deal Expert
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Nov 28, 2016
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Out west
barqers wrote: We hardly use it at all, it's only for items that accidentally make it down the drain into the garbage disposal. The odd thing is the dishwasher drains fine and connects into the sink drain that I can see in the basement. So it would have to be somewhere between the p-trap under the kitchen sink and where it connects to the dishwasher line. I might try snaking it again but snaking drain lines is such a pain.
Could be from years of the previous owner to. They suck, I hate them
Sr. Member
Dec 3, 2002
504 posts
38 upvotes
BC
barqers wrote: Thanks Rob - been trying the plunger for about 30 minutes this morning to no avail. Might try snaking it again before giving up and calling someone in. I tried vinegar/baking soda as well, plus dawn and boiling water, no luck so far.
I had the same issue with our kitchen sink.
Hot water and detergent didn't work.
We ended up using liquid declogger (Drano or equivalent). It luckily only took one application to clear whatever blockage was downstream.
Good luck.
Member
Mar 17, 2004
494 posts
56 upvotes
you can rent a professional snake thats way longer and has an electric motor that runs cutters that scrape the crap off your pipes as it goes. Those hand held units are only good for small clogs.
[OP]
Deal Addict
Jun 11, 2010
1500 posts
913 upvotes
ottawa
WikkiWikki wrote: Could be from years of the previous owner to. They suck, I hate them
It probably is... I found glass in it when I moved in as well as plastic from what looked like a peanut butter container. I actually do not like the disposal unit at all lol.
Starcraftjunkie wrote: I had the same issue with our kitchen sink.
Hot water and detergent didn't work.
We ended up using liquid declogger (Drano or equivalent). It luckily only took one application to clear whatever blockage was downstream.
Good luck.
dealhunting wrote: you can rent a professional snake thats way longer and has an electric motor that runs cutters that scrape the crap off your pipes as it goes. Those hand held units are only good for small clogs.
Thanks for all the replies - I've tried a couple more times with the handheld unit but got absolutely nowhere. I might try liquid declogger but I've read it can ruin your pipes? My entire house is all ABS no cast iron or steel so not sure if that makes a difference.
Deal Expert
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Nov 28, 2016
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Out west
barqers wrote: It probably is... I found glass in it when I moved in as well as plastic from what looked like a peanut butter container. I actually do not like the disposal unit at all lol.





Thanks for all the replies - I've tried a couple more times with the handheld unit but got absolutely nowhere. I might try liquid declogger but I've read it can ruin your pipes? My entire house is all ABS no cast iron or steel so not sure if that makes a difference.

If you need to do all this, and hate it. Nows the time to get rid of it. And you can use the power that is there for maybe some kicthen LED lighting, etc Free up some space underneath the sink as well
Deal Fanatic
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Dec 27, 2009
7691 posts
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Victoria, BC
Garburators were banned in Ottawa, right? I never saw one in all my years there. I double checked, and the wording doesn't even really grandfather use of old ones from before. It states they are not to be operated.
[OP]
Deal Addict
Jun 11, 2010
1500 posts
913 upvotes
ottawa
WikkiWikki wrote:
If you need to do all this, and hate it. Nows the time to get rid of it. And you can use the power that is there for maybe some kicthen LED lighting, etc Free up some space underneath the sink as well
Chickinvic wrote: Garburators were banned in Ottawa, right? I never saw one in all my years there. I double checked, and the wording doesn't even really grandfather use of old ones from before. It states they are not to be operated.
Good points - we don't use ours at all, only for particles that accidentally make their way down instead of in the compost bin. Managed to free the sink with about 1L of drano, 30 mins of waiting, and a LOT of plunging. Whenever we have to get the plumber out next we'll take the garburator out and have a new pipe put in.

Thanks everyone.
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Aug 20, 2021
1005 posts
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Toronto
dealhunting wrote: you can rent a professional snake thats way longer and has an electric motor that runs cutters that scrape the crap off your pipes as it goes. Those hand held units are only good for small clogs.
I am having a problem with my kitchen sink. Have used plunger and Drano several times and it still drains slowly. Maybe I will try renting a professional snake - how much are they to rent, and can anyone use them?

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