One complaint I hear from time to time is that a vessel sink will drain slowly. Obviously if the drain is plugged it will prevent water from draining properly. However if the drain is clear and the vessel still drains slowly what is the cause? Most vessel sinks don’t have an overflow drain. The overflow allows for more air to get into the drain which aids draining. Visualize pouring water out of a 2 litre bottle. It drains slowly. Now cut a hole in the bottom of the bottle and then pour the water out. With the hole in the bottle, air can enter the bottle and make the draining much faster. The grid drain seems to be the biggest cause of slow draining vessel sinks. This is because the water “sticks” to the grid. 
The surface tension of water becomes an issue with the small holes in the grid. It’s kind of like water on a widow screen. You notice that the water does not shed off of the tiny holes in the screen. The umbrella style drains seem to work better because the water mixes with air before it enters the drain.
If you are still having an issue with a slow drain, installing a studor vent on your drain may help. This device is a one way air valve that lets air go into the drain without letting any air out of the drain. These cost about $25 and are easy to install. Lastly, it is a good idea to adjust your faucet shut off valves so the flow of water to your faucet is reduced somewhat. This will minimalize splashing in your vessel sink and will allow your sink to empty a little quicker.
