Roof Deck Kitchen Sink Drain

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New Member
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Minneapolis MN
Hello all!
I am putting a outdoor kitchen on the roof of a condo building. I can run a new waste stack up though the roof for the drain, but I question the logical need. If I run the outdoor kitchen drain to the roof vent of a bar sink it would be much easier.
This line of thinking got me reading about the importance of vents, but my reading has not detailed the terrible consequences if I go to the dark side. I could see a "plug" of water rushing down the 2" vent and causing noise and displacement of the 1.5" trap on the bar sink, but its all in a vertical pipe and that seems unlikely. This 2" pipe only has a bar sink right now and I remain tempted...
Can you explain why the pressurization changes and hydraulic pressures of this ill advised idea won't work, or in what cases would this be a problem?



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John Gayewski

In the Trades
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It's self explanatory really and you explained it. The pipe being vertical is actually the problem and not a helpful thing as the velocity will be increased by a lot. The trap arm length on the bar sink below would be a factor too. If the trap arm is long it's less likley to siphon, but water/debris will run into this trap arm and potentially plug it. Especially this being a kitchen sink with food waste.

A plumber wouldn't do this, but it sounds like you've made up your mind.

Are you sure the vent pipe is totally vertical? Vent fittings aren't orientated for drainage and take turns that are not pitched at times also.
Hey, wait a minute.

This is awkward, but...

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