The drain line from my kitchen sink drops down through the basement, into the basement floor (Concrete), and I assume under the floor to the main sewer line. The sink tends to drain slowly. Should I have a separate vent at the sink, or is it OK if the only vent is the main vent stack?

Should I snake out the line to see if it helps, or is this more likely a problem with not having air behind water?


I have already taken apart and checked all the pipe that is above the basement floor (and it was clear), if there is a clog it would be in the line that runs under the basement floor.

3 Answers 3


To answer the specific question of whether you need a separate vent for this sink: in my state (VA), the allowable distance between a 1 1/2" drain trap (standard size for a kitchen sink) and its vent is 6 feet. If your trap is farther from the vent than that, then you should consider adding a new vent or an air admittance valve.

That said, too much distance from the vent won't cause your sink to drain slowly. The problem with it being too far away is that the column of water flowing away from the trap is large and heavy enough that it has the potential to suck the water out of your trap as it leaves. And along with this sucking comes the gurgling sounds mentioned in the other answers here.

EDIT: To be clear, your sink doesn't have to be 6 feet from the vent stack, i.e. the main vent pipe that goes through the roof. Your DWV system may have other vent pipes that converge in the attic at the main stack.


If there is a venting problem, you might hear gurgling when the sink drains, or perhaps see the water dip down in a toilet when you use your sink. From your description, this sounds more like a clogged drain. If only the sink drains slowly, then it a more likely a problem near that point.

I'd look at the sink. You might pull the elbow off under the sink. Is it clogged? That is a better place to use a snake from anyway, once this is opened up.

Be careful with chemical drain cleaners, as they can be quite nasty.

  • Sorry, should have mentioned the trap and drain is clear down to the clean out for the line that runs under the basement floor.
    – Tester101
    Commented Nov 10, 2010 at 14:01

Snaking might help, as might opening and cleaning the trap (if water is moving slowly, you're more likely to have solids settling out, causing the water to move even more slowly). Ideally you should have a vent at the kitchen sink too; AFAIK, it doesn't have to be dedicated to the sink so you could hook up to an existing vent if you have one nearby.

  • The only vent is the main vent stack (it's not a big house), which the drain eventually connects to.
    – Tester101
    Commented Nov 10, 2010 at 13:59

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