Issue with basement sink

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Timmed

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Hi all - I have a really weird problem I have been unable to diagnose. Typical ranch house built in 1963. There is a utility room on the first floor with a large sink. Directly below the utility room is a basement kitchen, also with a sink. The two sinks seem to share the same 2" drain pipe, which then travels under the basement floor to the sewer main.

Both sinks drain perfectly without impacting each other. However, if I fill that utility room sink upstairs and then drain it, water comes shooting up like a geyser in the basement sink below it. I've had the drain line professionally snaked so I don't think there is a clog.

That basement sink used to have some kind of 1-way check valve in the drain line, but I removed it thinking maybe that was the problem. When the check valve was in place the basement sink merely had water gurgle up into it, but now with it removed, the water really shoots up.

My theory is that dumping the upstairs drain might fill that down pipe with so much water that it tries to seek level, and pushes up through the basement sink. So in other words, if the water level in the drain pipe is above the sink in the basement, physics is going to push up the water seeking level.

Is it against code to have those 2 sinks sharing the same vertical drain line? Any ideas on how I might fix this? Thanks in advance, Tim
 

Reach4

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Is it against code to have those 2 sinks sharing the same vertical drain line?
No.

That basement sink used to have some kind of 1-way check valve in the drain line, but I removed it thinking maybe that was the problem. When the check valve was in place the basement sink merely had water gurgle up into it, but now with it removed, the water really shoots up.
Clearly the former owner had the same problem and came up with that unusual workaround.

You could run another drain line.

I wonder if the drain cleaning person could snake the line, where it turns from vertical to horizontal below the basement floor , better. Cutting a section of drain line out above the basement sink could give better cleanout access. I am not a plumber, but I did cut out a section of line for better cleaning access. Put the cut-out piece back in place with two flex couplings.

I did my drain cleaning with a Brasscraft medium drain bladder.
 

John Gayewski

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Likely a sanitary tee drain where there should have been a wye and revent (back vent).

I think I'd cut open the wall and repipe.

If you decide to cut open the wall share a picture and we'll tell you what we think.
 

Reach4

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The two sinks seem to share the same 2" drain pipe, which then travels under the basement floor to the sewer main.
The pipe may be 1-1/2 inch (1.90 OD) rather than 2 inch.
 

Timmed

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John - Not even a sanitary tee in the basement location, looks like it just got plumbed into a clean-out. Would that explain the behavior I'm seeing?
 

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John Gayewski

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What's that?
 

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John Gayewski

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I have seen what your seeing without filling the horizontal drain pipe at the bottom of a stack. A sanitary tee doesn't fight off water falling from above very well.
 

Timmed

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I have seen what your seeing without filling the horizontal drain pipe at the bottom of a stack. A sanitary tee doesn't fight off water falling from above very well.
Thanks again John. That pic is the piping for the basement sink. Was trying to show that it doesn't even have a sanitary tee, looks just like a 90 degree cleanout it's connected to.

So if I tore that cast iron out, the basement drain should either have a separate line to the sewer main, OR I could put a wye pipe off the main drainline to give the basement sink more protection.

Thanks Tim
 

Jeff H Young

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its a stoppage ! just because you got a 1/4 inch hole through it with a snake dosent mean its fixed
 
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