I have an in-line air vent under my kitchen sink. I am having a problem with water draining slowly. How can I tell if the air vent is operating properly? Do I just replace, if that doesn't help where else would I look to solve this problem? I have snaked the drain, used dran-o, etc!

Snake the drain line again. And again, and again if necessary until the blockage is cleared.

A line vent will not cause slow drainage. If a line vent fails it will cause the trap to be siphoned dry, not cause a slow drain.

Unscrew the vent temporarily and drain the sink. Any difference? If not, reinstall vent. If yes, replace vent. Is this a white "studor " vent or a spring vent?

Unscrew the vent temporarily and drain the sink. Any difference? If not, reinstall vent. If yes, replace vent. Is this a white "studor " vent or a spring vent?

It is a spring vent!

Snake the drain line again. And again, and again if necessary until the blockage is cleared.

A line vent will not cause slow drainage. If a line vent fails it will cause the trap to be siphoned dry, not cause a slow drain.

I snaked, snaked, snaked and snaked and it worked. Thanks!!

Congratulations.

Just for information. If this was an old galvanized drain and the chemicals like Draino were used before snaking, the chemicals probably worsened the blockage.

Imagine this. You have a blockage in the pipe. The interior walls of the pipe are coated with from 1/4 to 1/2" of sludge and gunk. You pour in a chemical that softens the sludge and gunk. The sludge and gunk collapses and falls down inside the pipe. Now you have a thick, soft, sticky substance in the pipe that can't flow out because of the original blockage.

Now you try snaking the pipe. The snake just passes through the soft sludge. Maybe you even break up the original blockage but when you pull the snake out the sludge just closes in to fill up the hole you just made through it.

Don't use chemicals in drain pipes.