Many in our condo. Complex have this problem. Hot water in the kitchen sink drains much slower then cold water. The drain has a line above the trap going to a dish washer.
Some have corrected this problem by adding a vent line. My question is "Why would hot water act different then cold water?" I was told that hot water expands the pipe causing this problem. I don't believe this.

When was your building built?

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Some have corrected this problem by adding a vent line.

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Are you saying the kitchens aren't vented? I can see no reason for the cold water to drain faster then hot.

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I was told that hot water expands the pipe causing this problem.

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If this were so the hot water would drain faster then the cold. Not that I believe for one second that a pipe that has hot water daining through it will expand enough to make a difference. Water drains by gravity and hot water will weigh as much as cold. It's a mystery to me! Any experts out there with a answer? Tom

Condo is new, 2006. The building is vented but the kitchen sink does not have its own separate drain.

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the kitchen sink does not have its own separate drain.

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Please explain! Thanks, Tom

New building and no separate vent for kitchen sink. This doesn't sound right. Hot water should drain the same as cold, as Tom said. Can you explain how the sink is vented.

Where have the other tenants added a vent that cured the problem?

I meant to say the kitchen sink does not have its own separate VENT. The other condos have put a vent under the sink. I don't know if it is above or below the trap. I have a feeling it has something to do with the dish washer draining into the same line. The condo has a vent on the roof and another before the sewer.

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I meant to say the kitchen sink does not have its own separate VENt.

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Where do you live that a inspector will C.O a building that doesn't vent every fixture vented? Inquiring minds want to know. Tom

I'm not a plumber so perhaps I'm not explaining myself correctly. This is a condominium complex of 300 units. I know for a fact that it is up to code.
My kitchen sink and dishwasher drain in a common pipe (about 2” dia,) to the basement where it go through a trap then to a waste line (about 4” dia.). This 4” line has a vent that goes to the roof. The 4” line continues through a large trap then to the sewer.
I'm assuming that this 4” vent is a “common” vent for all of the fixtures. Are you saying that every fixture should have its own separate vent to the roof?

Other tenants have most likely added aav's. The trap should be above floor, right under kitchen sink. If the vent is below flood rim, then it does no good. Really would like for you to post as many pics of the plumbing as possible.