And running a snake down the drain pipe.

I would suggest going to YouTube for some videos to follow that would explain it better than I can here.

It’s a long barbed plastic stick you can get at Lowe’s or other stores. Stick it down the sink and it will pull out all sorts of stuff. They say not to reuse it, likely because you could cut yourself on the barbs. But I rinse mine off and carefully dry it. I’ve had the same one for several years.

I hope they have them in stock for you. I haven’t checked lately. Good luck!

Let sit for half an hour and then pour boiling water.
I used about a cup of Clorox. Worked for me. Not sure what it did to the pipes.

Used that crap once, and ended up with a chemical burn on my hand that took months to heal.

Recommend removing the P-trap, and cleaning the entire pipe from the drain out to the wall stub.

Get a bucket out. Put it under p trap. Open o trap.

Then use a snake down and up

New information:

I believe there has been sewer/sludge back-up. When I pull up the plunger, black/grey putrid water and particles come up.

I have a fine-mesh screen over the drain to prevent food particles from going down. And this just happened last night.

I may need a plumber in case this goes into the wall.

Did you do a load of laundry last night? If not it sounds like a sink clog. Taking the p-trap apart is a pretty simple job. A pair of channel locks and some plumbers tape so it doesn’t leak when you put it back together.

It's a clog alright, but it's smelly black brackish water. I really think it's a sewer back up

Tub/shower drains are lower than all the sink drains. Guess it would depend on the plumbing but anywhere I’ve ever lived the tub backs up first, usually during the spin cycle on the washing machine.

if so you are not plunging the drain, but the other side of the sink. i use a second plunger to cover that second drain while i plunge the 1st one.

and smells a lot like sewage. It's old grease, hair, food waste, etc. that's rotting so yes, it really smells.

worry about that nasty stuff coming up into your sink.

He never bothered with better living through chemistry.

put a bucket under it. your zip may be enough or you may need a snake, for further along.

I called my Landlord who called a plumber.

1. It was sludge.
2. P-Trap cleared. Some drilling/snaking was necessary.
3. Was instructed to use baking-soda-vinegar-hot water every month, sort of like flossing the pipes.

Thanks for your support and responses.

I'm catching up on washing my dishes, pots, and pans.

Swears the corrosive ingredients in coke will clean out any drain. It's quick and cheap.