Slow sink drain

[Slir]

Hi all!
I recently replaced a double bowl sink with a single bowl. Underneath I have a garbage disposal, along with a dishwasher draining into the side of the disposal. Now the sink drains very slowly. No clogged pipes, no food in the disposal. When I turn on the garbage disposal, the water drains quickly. Any suggestions? Would a sink vent help?
If so, any guidelines on adding one? Any suggestions?
Thanks!

 

[Geofd]

You need to show pic some of the drain piping

 

[Slir]

You need to show pic some of the drain piping

 

[Jeff Handy]

You have an S trap, where the drain exits straight down through the cabinet floor.
This is a bad design, since it tends to suck itself dry by siphoning, when a large volume of water goes down there.

Then dangerous and smelly sewer gas comes right up out of your sink strainer, because the trap is dry.

There also does not seem to be a vent, which lets outside air from the roof help the drain to flow better.
Sometimes the vent comes in down below in the next room. Still not a good setup.

Meanwhile, it is very possible that your drain line is partially clogged somewhere, it could be close by or 30 feet away.

You can try using a drain cleaner like Instant Power from Home Depot, which does well in loosening up grease and food waste.

You also should add a Studor vent, also known as an AAV or cheater vent, to let room air get in behind the water that is trying to drain.
There are tons of Youtube videos showing how to do this.
Or a pro on here might give advice.

The sink water will drain faster, which will help flush mushy food waste and grease down into the larger main drain.

 

[Geofd]

There is no vent and that is an s trap
You need to change it to a p trap and were the p trap connects to the pipe going down you need to install an air admittance valve this takes the place of a conventional vent I can’t draw it so look it up and there will be examples