Problem with sink drain

[Manny Bhuta]

When kitchen sink - at least half full, is drained, the water backs up in to a sink in the basement. There is no problem if I run the kitchen faucet without stopping the drain. The kitchen sink is vented but the sink in the basement is not. Is there any way to resolve this problem? Venting the sink in the basement is not practical. The basement sink seems to drain well. I was wondering if there is such a thing as one way valve that I can install in the basement sink drain.

[Mark M.]

To prevent siphoning of the trap, an air admittance valve (mechanical vent) lets air into the drain line. In addition to admitting air, a conventional vent also lets air out. Your basement sink is backing up not because air can't get in but because the air ahead of the draining water can't get out. This means an air admittance valve won't help. What you need on your basement sink is a vent that leads all the way through the roof. If you tie it in to an existing vent it must connect no lower than 6" above the flood rim of the highest fixture served by that vent.

Mark M.

[Manny Bhuta]

Thanks Mark. I was afraid that a proper vent is the only solution. Unfortunately it is rather impractical. I guess I will have to either live with the issue or remove the sink in the basement.

Manny