A single vent is down the middle A double vent has a vent near the sides

There is a vent available for this. It is meant to cap 1 1/2 PVC. T the drain and put the vent as high as you can. It is spring loaded and the water will pull the vent open and close when the pressure equalizes. This is only for a single sink. If using a double sink, one side uses the other for the vent. You can use the add on with a double, you just don't have to.

The vent for the drain is in the wall. Where the drain goes in, it T's with the water going down and the vent going through the roof. With a double sink, one side is the vent for the other. As long as the water isn't pulling against a vacuum, it will drain.

A double sided naginata.

the stvenson screen has a air vent on the top of it so that air can get out