Hello,

I'm having an unusual plumbing issue. When draining a full or half full kitchen sink I can see water trikling down on the cement basement wall and some water coming out of the drain hole between wall and floor of the basement - all directly below the kitchen sink.
Now this only happens when a large amount of water is draining, there is no water leak in the basement at all when running a kitchen faucet or a dishwasher.
There is a slight gurgling sound when large amount of water is draining and I actually see a little bit of water on the cabinet floor directly under the sink and to the right (the drain pipe goes from the sink to the right).

I was told that the issue can be a clogged air vent or even a disconnected air vent between the kitchen sink and the roof vent.

Is that an accurate diagnosis of the problem or there might be something else.

Thanks

Is that an accurate diagnosis of the problem
I doubt it. You have a leak, a leak at a joint some where in the drain line. That leak will probably be in a vertical joint where the upper pipe fits into a coupling. When you open a faucet the water runs out the drain, but there is only so much water. When you empty the sink the water flows out at a much greater volume and fills the drain pipe, backs up at the joint and leaks out the upper joint.

I actually see a little bit of water on the cabinet floor directly under the sink and to the right (the drain pipe goes from the sink to the right).
If the drain goes to the right and then down, the leak is probably close to that point.

hkstroud - thank you very much for a quick response.

If the leak is in the drain pipe wouldn't the water come out regardless when the faucet is turned all the way on? I would think there would be at least a trickle somewhere - and there isn't. The backup seems to be in the air pipe since that is where the extra volume of water would go.

I agree there is a difference in volume between an open faucet and a half full sink but I would think the leak would always have water coming out just in smaller amounts.

First, my drawings take a lot of imagination.
Second, pipes fit inside of fittings.
Third, water flows through a vertical pipe faster than through a horizontal pipe. Therefore water flowing horizontal at full capacity will back up into a vertical section of pipe.
If this is old plumbing and galvanized piping you probably have partial blockage and you have a rusted out joint. If this is relatively new plumbing with PVC pipe, the plumber forgot to glue the upper side of a joint somewhere. That joint could be where the vent ties in but it is not caused by a blocked vent pipe.
Only way to fix is to open up the walls and look. You should know the leaking joint when you see it. If you have a leak inside the cabinet where the pipe goes into the wall that's where the leak most likely at just inside the wall where the drain meets the vent.

Water won't back up a vent pipe unless there is a blockage or at least a partial blockage somewhere.