During our kitchen remodel, we replaced our double sink with a single bowl. There was no drainage issue before the remodel, now it drains really slowly. The drain was open for 2 months during the remodel, uncovered, with no sewer gas odor. Dishwasher drain enters just below the sink, followed by a p-trap. Drain pipe goes through the floor into the basement and runs along the ceiling, emptying into the main drain about 20 feet away. An old vent pipe branches horizontally from the sink drain about 10 feet and a couple of turns down the line, but it was disconnected and capped off in the basement years ago, before I lived here. I added an aav vent under the sink, to the top of the vertical pipe that goes through the floor, 5 inches above the horizontal pipe from the p-trap. No help. I snaked 25 feet. No help. I used drain cleaner. No help. 2 other sinks and a washer empty into the same part of the main drain line with no issues. I don't know what else to try. Anyone have any ideas?
The problem here is that now with just a single drain hole you are experiencing a suction lock as a sink full of water tries to go down the drain. It will most likely require the relocation or addition of another sewer vent pipe up through the roof near this sink to break the suction path.
Install a cheater valve, as Kathy said or other wise known as an AAV air admittance unit, very easy to do if u have basic plumbing experience u can google it, if not calls plumber very quick and cheap for them to do