I have a double bowl sink in the kitchen. The drainage runs out directy below one tub. I have lived in the house 10 years and have always had slow draining out of the other tub. I have tried several times to clean out the slow drain but to no avail. I have taken the plumbing out under the sink and have found nothing that would slow the drain. I also see nothing that looks like a vent of any kind so I'm guessing the builder did not install one. Which doesn't surprise me, he didn't install shut off valves at any of the sinks in the house either. So when I needed to work on a sink I had to shut the water off to the entire house.

Someone mentioned that installing an air admittance vent would help alleviate the issue so here are my questions:

1. Will installing the Air admittance vent help with the draining of the second tub?
2. Where should the vent itself be installed?

I appreciate any help/guidance you guys/gals can provide.